Runs of homozygosity in European populations

Insights from homozygous signatures of cervus nippon revealed genetic architecture for components of fitness

This study investigates the genomic landscape of Sika deer populations, emphasizing the detection and characterization of runs of homozygosity (ROH) and their contribution towards components of fitness. Using 85,001 high-confidence SNPs, the investigation into ROH distribution unveiled nuanced patterns of autozygosity across individuals especially in 2 out of the 8 farms, exhibiting elevated ROH levels and mean genome coverage under ROH segments. The prevalence of shorter ROH segments (0.5-4 Mb) suggests historical relatedness and potential selective pressures within these populations. Intriguingly, despite observed variations in ROH profiles, the overall genomic inbreeding coefficient (FROH) remained relatively low across all farms, indicating a discernible degree of genetic exchange and effective mitigation of inbreeding within the studied Sika deer populations. Consensus ROH (cROH) were found to harbor genes for important functions viz., EGFLAM gene which is involved in the vision function of the eye, SKP2 gene which regulates cell cycle, CAPSL involved in adipogenesis, SPEF2 which is essential for sperm flagellar assembly, DCLK3 involved in the heat stress. This first ever study on ROH in Sika deer, to shed light on the adaptive role of genes in these homozygous regions. The insights garnered from this study have broader implications in the management of genetic diversity in this vulnerable species.

Selection signatures for high altitude adaptation in livestock: A review

High altitude adapted livestock species (cattle, yak, goat, sheep, and horse) has critical role in the human socioeconomic sphere and acts as good source of animal source products including milk, meat, and leather, among other things. These species sustain production and reproduction even in harsh environments on account of adaptation resulting from continued evolution of beneficial traits. Selection pressure leads to various adaptive strategies in livestock whose footprints are evident at the different genomic sites as the "Selection Signature". Scrutiny of these signatures provides us crucial insight into the evolutionary process and domestication of livestock adapted to diverse climatic conditions. These signatures have the potential to change the sphere of animal breeding and further usher the selection programmes in right direction. Technological revolution and recent strides made in genomic studies has opened the routes for the identification of selection signatures. Numerous statistical approaches and bioinformatics tools have been developed to detect the selection signature. Consequently, studies across years have identified candidate genes under selection region found associated with numerous traits which have a say in adaptation to high-altitude environment. This makes it pertinent to have a better understanding about the selection signature, the ways to identify and how to utilize them for betterment of livestock populations as well as farmers. This review takes a closer look into the general concept, various methodologies, and bioinformatics tools commonly employed in selection signature studies and summarize the results of recent selection signature studies related to high-altitude adaptation in various livestock species. This review will serve as an informative and useful insight for researchers and students in the field of animal breeding and evolutionary biology.

Best practices for germline variant and DNA methylation analysis of second- and third-generation sequencing data

This comprehensive review provides insights and suggested strategies for the analysis of germline variants using second- and third-generation sequencing technologies (SGS and TGS). It addresses the critical stages of data processing, starting from alignment and preprocessing to quality control, variant calling, and the removal of artifacts. The document emphasized the importance of meticulous data handling, highlighting advanced methodologies for annotating variants and identifying structural variations and methylated DNA sites. Special attention is given to the inspection of problematic variants, a step that is crucial for ensuring the accuracy of the analysis, particularly in clinical settings where genetic diagnostics can inform patient care. Additionally, the document covers the use of various bioinformatics tools and software that enhance the precision and reliability of these analyses. It outlines best practices for the annotation of variants, including considerations for problematic genetic alterations such as those in the human leukocyte antigen region, runs of homozygosity, and mitochondrial DNA alterations. The document also explores the complexities associated with identifying structural variants and copy number variations, underscoring the challenges posed by these large-scale genomic alterations. The objective is to offer a comprehensive framework for researchers and clinicians, ensuring that genetic analyses conducted with SGS and TGS are both accurate and reproducible. By following these best practices, the document aims to increase the diagnostic accuracy for hereditary diseases, facilitating early diagnosis, prevention, and personalized treatment strategies. This review serves as a valuable resource for both novices and experts in the field, providing insights into the latest advancements and methodologies in genetic analysis. It also aims to encourage the adoption of these practices in diverse research and clinical contexts, promoting consistency and reliability across studies.

Exploring the human genomic landscape: patterns of common homozygosity regions in a large middle eastern cohort

Regions of Homozygosity (ROH) typically reflect normal demographic history of a human population, but may also relate to cryptic consanguinity, and, additionally, have been associated with specific medical conditions. The objective of this study was to investigate the location, size, and prevalence of common ROH segments in a Middle Eastern cohort. This retrospective study included 13 483 samples collected from all Chromosomal Microarray analyses (CMA) performed using Single Nucleotide Polymorphism (SNP) arrays at the genetic clinical laboratory of Rabin Medical Center between 2017-2023 (primary data set). An additional replication cohort including 100 842 samples from another SNP array platform, obtained from Maccabi Health Organization, was analyzed. Common ROH locations were defined as those ROH locations involving 1% or more of the samples. A total of 66 710 ROH segments, involving 13 035 samples (96.7%) were identified in the primary data set. Of the 4069 cytogenetic ROH locations, 68 were identified as common. The prevalence of non-common ROH was relatively high in affected individuals, and for acrocentric chromosomes, chromosomes associated with common trisomies, and non-imprinted chromosomes. In addition, differences in common ROH locations were observed between the primary and the replication cohorts. Our findings highlight the need for population-specific guidelines in determining ROH reporting cutoffs, considering factors such as population-specific prevalence and testing platform differences. Future research with larger, varied cohorts is essential to advance understanding of ROH's associations with medical conditions and to improve clinical practices accordingly.

Phylogenetic Relations and High-Altitude Adaptation in Wild Boar (Sus scrofa), Identified Using Genome-Wide Data

The Qinghai-Tibet Plateau (QTP) wild boar is an excellent model for investigating high-altitude adaptation. In this study, we analyzed genome-wide data from 93 wild boars compiled from various studies worldwide, including the QTP, southern and northern regions of China, Europe, Northeast Asia, and Southeast Asia, to explore their phylogenetic patterns and high-altitude adaptation based on genome-wide selection signal analysis and run of homozygosity (ROH) estimation. The findings demonstrate the alignment between the phylogenetic associations among wild boars and their geographical location. An ADMIXTURE analysis indicated a relatively close genetic relationship between QTP and southern Chinese wild boars. Analyses of the fixation index and cross-population extended haplotype homozygosity between populations revealed 295 candidate genes (CDGs) associated with high-altitude adaptation, such as TSC2, TELO2, SLC5A1, and SLC5A4. These CDGs were significantly overrepresented in pathways such as the mammalian target of rapamycin signaling and Fanconi anemia pathways. In addition, 39 ROH islands and numerous selective CDGs (e.g., SLC5A1, SLC5A4, and VCP), which are implicated in glucose metabolism and mitochondrial function, were discovered in QTP wild boars. This study not only assessed the phylogenetic history of QTP wild boars but also advanced our comprehension of the genetic mechanisms underlying the adaptation of wild boars to high altitudes.

Inbreeding Effect on Maternal Mortality and Fertility in the Habsburg Dynasty

OBJECTIVE

We investigated inbreeding effects on longevity and fertility in the House of Habsburg, one of the principal royal dynasties of Europe.

METHODS

A total number of 124 Habsburg marriages, involving 107 men and 124 women, in the period of approximately 1450-1800 were considered for the analysis. Kinship and inbreeding coefficients were computed from genealogical information, which included more than 8000 individuals.

RESULTS

We found a significant negative association between age of death and inbreeding coefficient (F) in those women who had children (regression coefficient b = -1.06, p = 0.0008). This result led us to investigate possible inbreeding effects on maternal mortality in the period of 4 weeks after the childbirth. A strong inbreeding depression on maternal survival was detected through the Kaplan-Meier curve for groups of women with different level of inbreeding (log-rank test p = 0.0001) and the Cox proportional hazards regression analysis (hazard ratio = 2.36, p = 0.0008). Effect on fertility was also found as more inbred women had longer interbirth intervals (b = 154.66, p = 0.022). Effects of male or female inbreeding on the number of children per woman were not detected through zero-inflated regression models suggesting that reproductive compensation might be occurring among the more inbred and less-fecund women.

CONCLUSION

The effect of inbreeding in adulthood in the Habsburg lineage was at least as important as that previously reported on prereproductive survival. To our knowledge, our results are the first evidence of an inbreeding effect on maternal mortality in humans.

Too big to purge: persistence of deleterious Mutations in Island populations of the European Barn Owl (Tyto alba)

A key aspect of assessing the risk of extinction/extirpation for a particular wild species or population is the status of inbreeding, but the origin of inbreeding and the current mutational load are also two crucial factors to consider when determining survival probability of a population. In this study, we used samples from 502 barn owls from continental and island populations across Europe, with the aim of quantifying and comparing the level of inbreeding between populations with differing demographic histories. In addition to comparing inbreeding status, we determined whether inbreeding is due to non-random mating or high co-ancestry within the population. We show that islands have higher levels of inbreeding than continental populations, and that this is mainly due to small effective population sizes rather than recent consanguineous mating. We assess the probability that a region is autozygous along the genome and show that this probability decreased as the number of genes present in that region increased. Finally, we looked for evidence of reduced selection efficiency and purging in island populations. Among island populations, we found an increase in numbers of both neutral and deleterious minor alleles, possibly as a result of drift and decreased selection efficiency but we found no evidence of purging.

Assessment of inbreeding coefficients and inbreeding depression on complex traits from genomic and pedigree data in Nelore cattle

BACKGROUND

Nelore cattle play a key role in tropical production systems due to their resilience to harsh conditions, such as heat stress and seasonally poor nutrition. Monitoring their genetic diversity is essential to manage the negative impacts of inbreeding. Traditionally, inbreeding and inbreeding depression are assessed by pedigree-based coefficients (F), but recently, genetic markers have been preferred for their precision in capturing the inbreeding level and identifying animals at risk of reduced productive and reproductive performance. Hence, we compared the inbreeding and inbreeding depression for productive and reproductive performance traits in Nelore cattle using different inbreeding coefficient estimation methods from pedigree information (FPed), the genomic relationship matrix (FGRM), runs of homozygosity (FROH) of different lengths (> 1 Mb (genome), between 1 and 2 Mb - FROH 1-2; 2-4 Mb FROH 2-4 or > 8 Mb FROH >8) and excess homozygosity (FSNP).

RESULTS

The correlation between FPed and FROH was lower when the latter was based on shorter segments (r = 0.15 with FROH 1-2, r = 0.20 with FROH 2-4 and r = 0.28 with FROH 4-8). Meanwhile, the FPed had a moderate correlation with FSNP (r = 0.47) and high correlation with FROH >8 (r = 0.58) and FROH-genome (r = 0.60). The FROH-genome was highly correlated with inbreeding based on FROH>8 (r = 0.93) and FSNP (r = 0.88). The FGRM exhibited a high correlation with FROH-genome (r = 0.55) and FROH >8 (r = 0.51) and a lower correlation with other inbreeding estimators varying from 0.30 for FROH 2-4 to 0.37 for FROH 1-2. Increased levels of inbreeding had a negative impact on the productive and reproductive performance of Nelore cattle. The unfavorable inbreeding effect on productive and reproductive traits ranged from 0.12 to 0.51 for FPed, 0.19-0.59 for FGRM, 0.21-0.58 for FROH-genome, and 0.19-0.54 for FSNP per 1% of inbreeding scaled on the percentage of the mean. When scaling the linear regression coefficients on the standard deviation, the unfavorable inbreeding effect varied from 0.43 to 1.56% for FPed, 0.49-1.97% for FGRM, 0.34-2.2% for FROH-genome, and 0.50-1.62% for FSNP per 1% of inbreeding. The impact of the homozygous segments on reproductive and performance traits varied based on the chromosomes. This shows that specific homozygous chromosome segments can be signs of positive selection due to their beneficial effects on the traits.

CONCLUSIONS

The low correlation observed between FPed and genomic-based inbreeding estimates suggests that the presence of animals with one unknown parent (sire or dam) in the pedigree does not account for ancient inbreeding. The ROH hotspots surround genes related to reproduction, growth, meat quality, and adaptation to environmental stress. Inbreeding depression has adverse effects on productive and reproductive traits in Nelore cattle, particularly on age at puberty in young bulls and heifer calving at 30 months, as well as on scrotal circumference and body weight when scaled on the standard deviation of the trait.

[Runs of Homozygosity Decipher Genetic Diversity in Cattle Breed Dwelling in the Colder Regions of the World]

BACKGROUND

Our study focuses on Yakutian cattle, a Siberian native breed, examining its inbreeding and diversity through genome-wide analysis of runs of homozygosity (ROHs). Yakutian cattle are adapted to Siberia's harsh sub-arctic conditions, enduring temperatures below -70°C. However, the population genetics studies on this breed are scanty, to document the genetic uniqueness in these cattle.

RESULTS

We analyzed 40 Yakutian cattle with strict quality control for ROH detection yielding 683 homozygous segments, averaging 17 per individual with an average length of 9 Mb. ROH regions were found to be involved in important pathways pertaining to cold adaptation. Autozygosity ranged from 1% to 12% of the genome, with a relatively low average inbreeding coefficient (FROH) of 0.057, as compared to other breeds. Also, the different diversity indicators, namely, principal component analysis, heterozygosity, and effective population size analysis, revealed the prevalence of genetic diversity within the breed.

CONCLUSION

Our findings on ROH are the first of its kind in Yakutian cattle that support their adaptability to colder environments, as evidenced by low inbreeding and high genetic diversity.

Analyses of whole-genome sequences from 185 North American Thoroughbred horses, spanning 5 generations

Whole genome sequences (WGS) of 185 North American Thoroughbred horses were compared to quantify the number and frequency of variants, diversity of mitotypes, and autosomal runs of homozygosity (ROH). Of the samples, 82 horses were born between 1965 and 1986 (Group 1); the remaining 103, selected to maximize pedigree diversity, were born between 2000 and 2020 (Group 2). Over 14.3 million autosomal variants were identified with 4.5-5.0 million found per horse. Mitochondrial sequences associated the North American Thoroughbreds with 9 of 17 clades previously identified among diverse breeds. Individual coefficients of inbreeding, estimated from ROH, averaged 0.266 (Group 1) and 0.283 (Group 2). When SNP arrays were simulated using subsets of WGS markers, the arrays over-estimated lengths of ROH. WGS-based estimates of inbreeding were highly correlated (r > 0.98) with SNP array-based estimates, but only moderately correlated (r = 0.40) with inbreeding based on 5-generation pedigrees. On average, Group 1 horses had more heterozygous variants (P < 0.001), more total variants (P < 0.001), and lower individual inbreeding (FROH; P < 0.001) than horses in Group 2. However, the distribution of numbers of variants, allele frequency, and extent of ROH overlapped among all horses such that it was not possible to identify the group of origin of any single horse using these measures. Consequently, the Thoroughbred population would be better monitored by investigating changes in specific variants, rather than relying on broad measures of diversity. The WGS for these 185 horses is publicly available for comparison to other populations and as a foundation for modeling changes in population structure, breeding practices, or the appearance of deleterious variants.

Regionally enriched rare deleterious exonic variants in the UK and Ireland

It is unclear how patterns of regional genetic differentiation in the UK and Ireland might impact the protein-coding fraction of the genome. We exploit UK Biobank (UKB) and Viking Genes whole exome sequencing data to study regional genetic differentiation across the UK and Ireland in protein coding genes, encompassing 44,696 unrelated individuals from 20 regions of origin. We demonstrate substantial exonic differentiation among Shetlanders, Orcadians, individuals with full or partial Ashkenazi Jewish ancestry and in several mainland regions (particularly north and south Wales, southeast Scotland and Ireland). With stringent filtering criteria, we find 67 regionally enriched (≥5-fold) variants likely to have adverse biomedical consequences in homozygous individuals. Here, we show that regional genetic variation across the UK and Ireland should be considered in the design of genetic studies and may inform effective genetic screening and counselling.

Whole-genome resequencing identifies candidate genes associated with heat adaptation in chickens

The wide distribution and diverse varieties of chickens make them important models for studying genetic adaptation. The aim of this study was to identify genes that alter heat adaptation in commercial chicken breeds by comparing genetic differences between tropical and cold-resistant chickens. We analyzed whole-genome resequencing data of 186 chickens across various regions in Asia, including the following breeds: Bian chickens (B), Dagu chickens (DG), Beijing-You chickens (BY), and Gallus gallus jabouillei from China; Gallus gallus murghi from India; Vietnam native chickens (VN); Thailand native chickens (TN) and Gallus gallus spadiceus from Thailand; and Indonesia native chickens (IN), Gallus gallus gallus, and Gallus gallus bankiva from Indonesia. In total, 5,454,765 SNPs were identified for further analyses. Population genetic structure analysis revealed that each local chicken breed had undergone independent evolution. Additionally, when K = 5, B, BY, and DG chickens shared a common ancestor and exhibited high levels of inbreeding, suggesting that northern cold-resistant chickens are likely the result of artificial selection. In contrast, the runs of homozygosity (ROH) and the ROH-based genomic inbreeding coefficient (FROH) results for IN, TN, and VN chickens showed low levels of inbreeding. Low population differentiation index values indicated low differentiation levels, suggesting low genetic diversity in tropical chickens, implying increased vulnerability to environmental changes, decreased adaptability, and disease resistance. Whole-genome selection sweep analysis revealed 69 candidate genes, including LGR4, G6PC, and NBR1, between tropical and cold-resistant chickens. The genes were further subjected to GO and KEGG enrichment analyses, revealing that most of the genes were primarily enriched in biological synthesis processes, metabolic processes, central nervous system development, ion transmembrane transport, and the Wnt signaling pathway. Our study identified heat adaptation genes and their functions in chickens that primarily affect chickens in high-temperature environments through metabolic pathways. These heat-resistance genes provide a theoretical basis for improving the heat-adaptation capacity of commercial chicken breeds.

Detectability of runs of homozygosity is influenced by analysis parameters and population-specific demographic history

Wild populations are increasingly threatened by human-mediated climate change and land use changes. As populations decline, the probability of inbreeding increases, along with the potential for negative effects on individual fitness. Detecting and characterizing runs of homozygosity (ROHs) is a popular strategy for assessing the extent of individual inbreeding present in a population and can also shed light on the genetic mechanisms contributing to inbreeding depression. Here, we analyze simulated and empirical datasets to demonstrate the downstream effects of program selection and long-term demographic history on ROH inference, leading to context-dependent biases in the results. Through a sensitivity analysis we evaluate how various parameter values impact ROH-calling results, highlighting its utility as a tool for parameter exploration. Our results indicate that ROH inferences are sensitive to factors such as sequencing depth and ROH length distribution, with bias direction and magnitude varying with demographic history and the programs used. Estimation biases are particularly pronounced at lower sequencing depths, potentially leading to either underestimation or overestimation of inbreeding. These results are particularly important for the management of endangered species, as underestimating inbreeding signals in the genome can substantially undermine conservation initiatives. We also found that small true ROHs can be incorrectly lumped together and called as longer ROHs, leading to erroneous inference of recent inbreeding. To address these challenges, we suggest using a combination of ROH detection tools and ROH length-specific inferences, along with sensitivity analysis, to generate robust and context-appropriate population inferences regarding inbreeding history. We outline these recommendations for ROH estimation at multiple levels of sequencing effort, which are typical of conservation genomics studies.

Runs of homozygosity analysis for selection signatures in the Yellow Korean native chicken

OBJECTIVE

Yellow Korean native chicken (KNC-Y) is one of the five pure Korean indigenous chicken breeds that were restored through a government project in 1992. KNC-Y is recognized for its superior egg production performance compared to other KNC lines. In this study, we performed runs of homozygosity (ROH) analysis to discover selection signatures associated with egg production traits in the KNC-Y population.

METHODS

A total of 675 DNA samples from KNC-Y were genotyped to generate single nucleotide polymorphism (SNP) data using custom 60K Affymetrix SNP chips. ROH analysis was performed using PLINK software, with predefined parameters set for the analysis. The threshold of ROH island was defined as the top 1% frequency of SNPs withing the ROH among the population.

RESULTS

In the KNC-Y population, a total of 29,958 runs of homozygosity (ROH) fragments were identified. The average total length of ROH was 120.84 Mb, with each ROH fragment having an average length of 2.71 Mb. The calculated ROH-based inbreeding coefficient (FROH) was 0.13. Furthermore, we revealed the presence of ROH islands on chromosomes 1, 2, 4, 5, 7, 8, and 11. Within the identified regions, a total of 111 genes were annotated, and among them were genes related to economic traits, including PRMT3, ANO5, HDAC4, LSS, PLA2G4A, and PTGS2. Most of the overlapping quantitative trait locus regions with ROH islands were found to be associated with production traits.

CONCLUSION

This study conducted a comprehensive analysis of ROH in the KNC-Y population. Notably, among the findings, the PTGS2 gene is believed to play a crucial role in influencing the laying performance of KNC-Y.

A comparison of genomic diversity and demographic history of the North Atlantic and Southwest Atlantic southern right whales

Right whales (genus Eubalaena) were among the first, and most extensively pursued, targets of commercial whaling. However, understanding the impacts of this persecution requires knowledge of the demographic histories of these species prior to exploitation. We used deep whole genome sequencing (~40×) of 12 North Atlantic (E. glacialis) and 10 Southwest Atlantic southern (E. australis) right whales to quantify contemporary levels of genetic diversity and infer their demographic histories over time. Using coalescent- and identity-by-descent-based modelling to estimate ancestral effective population sizes from genomic data, we demonstrate that North Atlantic right whales have lived with smaller effective population sizes (Ne) than southern right whales in the Southwest Atlantic since their divergence and describe the decline in both populations around the time of whaling. North Atlantic right whales exhibit reduced genetic diversity and longer runs of homozygosity leading to higher inbreeding coefficients compared to the sampled population of southern right whales. This study represents the first comprehensive assessment of genome-wide diversity of right whales in the western Atlantic and underscores the benefits of high coverage, genome-wide datasets to help resolve long-standing questions about how historical changes in effective population size over different time scales shape contemporary diversity estimates. This knowledge is crucial to improve our understanding of the right whales' history and inform our approaches to address contemporary conservation issues. Understanding and quantifying the cumulative impact of long-term small Ne, low levels of diversity and recent inbreeding on North Atlantic right whale recovery will be important next steps.

Assessment of genetic diversity, inbreeding and collection completeness of Jersey bulls in the US National Animal Germplasm Program

Genomic selection and extensive use of a few elite bulls through artificial insemination are leading to reduced genetic diversity in Jersey cattle. Conservation of genetic diversity through gene banks can protect a breed's genetic diversity and genetic gain, ensuring continued genetic advancement in the future. The availability of genomic information in the US National Animal Germplasm Program (NAGP) facilitates characterization of Jersey bulls in the germplasm collection. Therefore, in this study, we compared the genetic diversity and inbreeding between Jersey bulls in the NAGP and the national cooperator database (NCD). The NCD is maintained and curated by the Council on Dairy Cattle Breeding (CDCB). We found the genetic diversity to be marginally higher in NAGP (Ho = 0.34 ± 0.17) relative to the NCD population (Ho = 0.33 ± 0.16). The average pedigree and genomic inbreeding (FPED, FGRM, FROH > 2Mb) were similar between the groups, with estimates of 7.6% with FPED, 11.07% with FGRM and 20.13% with FROH > 2Mb. An increasing trend in inbreeding was detected, and a significantly higher level of inbreeding was estimated among the older bulls in the NAGP collection, suggesting an overrepresentation of the genetics from elite bulls. Results from principal component analyses (PCA) provided evidence that the NAGP collection is representative of the genetic variation found in the NCD population and a broad majority of the loci segregating (98.2%) in the NCD population were also segregating in the NAGP. Ward's clustering was used to assess collection completeness of Jerseys in the NAGP by comparison with top 1000 sires of bulls, top 1000 sires of cow, and bulls with high Lifetime Net Merit (NM$). All the clusters were represented in the NAGP suggesting that most of the genetic diversity in the US Jersey population is represented in the NAGP and confirmed the PCA results. The decade of birth was the major driver grouping bulls into clusters, suggesting the importance of selection over time. Selection signature analysis between the historic bulls in the NAGP with the newer bulls, born in the decade after implementation of genomic selection, identified selection for milk production, fat and protein yield, fertility, health, and reproductive traits. Cluster analysis revealed that the NAGP has captured allele frequency changes over time associated with selection, validating the strategy of repeated sampling and suggests that the continuation of a repeated sampling policy is essential for the germplasm collection to maintain its future utility. While NAGP should continue to collect bulls that have large influence on the population due to selection, care should be taken to include the entire breadth of bulls, including low merit bulls.

Genome-Wide Association Study (GWAS) for Left Displaced Abomasum in Highly Productive Russian Holstein Cattle

Left displaced abomasum (LDA) is a multifactorial disease of cattle that occurs mainly during the transition postpartum period and is characterized by a decrease in milk production and an increased risk of culling. Several studies have been conducted confirming the hereditary nature of predisposition to this disease. The aim of our study is to identify genetic associations characterizing the genomic variability of susceptibility to LDA in Holstein cattle of the Leningrad region of the Russian Federation. The objects of this study were 360 highly productive dairy cows divided into two groups: animals with LDA, and healthy ones (control). Runs of homozygosity analysis revealed one ROH on BTA13 that was found to be significantly more prevalent in the group of animals with LDA than in the healthy group. Fourteen candidate SNPs were found to be nominally associated with left displacement of the abomasum (p-value < 1 × 10-4). When performing functional annotation of genes containing associated polymorphisms or located close to them, candidate genes presumably associated with the development of LDA were identified: ABCB11, SRP72, RGS18, SOX4, GSG1L, FBXL19, and PNPLA4.

Analysis of the Genetic Diversity and Genetic Structure of Jiangshan Black Pigs Using Single Nucleotide Polymorphism (SNP) Chips

The Jiangshan black pig is an indigenous pig breed in China, renowned for its superior meat quality and adaptability to roughage. However, the population of Jiangshan black pigs has dwindled due to the introduction of cosmopolitan pig breeds and the outbreak of African swine fever, putting them at risk of extinction. To offer insights into the conservation and breeding of Jiangshan black pigs, this study involved 118 Jiangshan black pigs as the research subjects and employed the Zhongxin-1 Porcine Breeding Array PLUS chip to detect whole-genome SNPs. Additionally, various software tools were utilized to accurately analyze the genetic diversity, phylogenetic relationship, inbreeding coefficient, and pedigree structure of the Jiangshan black pig conservation population. The findings indicated that the effective population size (Ne) of the Jiangshan black pig was 4.9, with an average inbreeding coefficient of 0.253 within the population. A genetic relationship analysis identified that the 16 male pigs were clustered into four families, and the 100 female pigs were also assigned to these familial groups. Furthermore, two female pigs were classified as "other" due to their distant genetic relatedness to all the males. These results contribute to a better understanding of the current status of the conservation of the Jiangshan black pig population and offer a theoretical foundation for the development of conservation strategies.

Genetic structure, selective characterization and specific molecular identity cards of high-yielding Houdan chickens based on genome-wide SNP

The high-yielding Houdan chicken (GGF) is characterized by high egg production and disease resistance. This study conducted whole genome resequencing of the GGF population and compared it to data from other breeds. Genetic diversity analysis revealed higher observed heterozygosity (Ho), Polymorphism information content (PIC), number of runs of homozygosity (ROH), and inbreeding coefficient (FROH) in GGF. Linkage disequilibrium (LD) decay was slowest in GGF, indicating intensive inbreeding and strong selection. These findings suggest a need for appropriate strategies to enhance genetic diversity conservation in this breed. Population structure analysis demonstrated that GGF was genetically distinct from both the red jungle fowl (RJF) and Chinese indigenous chicken (CIC) populations, highlighting GGF as a unique genetic resource warranting intensive protection and utilization. Selective sweep analysis identified genes under selection in GGF, primarily enriched in signaling pathways related to oocyte meiosis and progesterone-mediated oocyte maturation. Key candidate genes included: CCNE1, SKP1, CDC20, CDK2, ADCY8, RPS6KA6, PPP3CB, PDE3B, HSP90AB1, and AKT3. These findings provide a theoretical foundation for their potential application in poultry breeding. Additionally, this study combined bioinformatics analysis with PCR amplification and Sanger sequencing to identify 4 SNPs that can serve as a molecular identity card (ID) for GGF: SNP1 (Chr2: 136130976), SNP3 (Chr4:11705164), SNP4 (Chr4: 63255588), and SNP5 (Chr24: 3271008). This study provides a scientific basis for effective management and conservation of GGF genetic resources, and establishes a simple, economical, and accurate set of molecular IDs to combat the proliferation of inferior breeds and protect genetic resources.

Genomic and Conventional Inbreeding Coefficient Estimation Using Different Estimator Models in Korean Duroc, Landrace, and Yorkshire Breeds Using 70K Porcine SNP BeadChip

The purpose of this study was to estimate the homozygosity distribution and compute genomic and conventional inbreeding coefficients in three genetically diverse pig breed populations. The genomic and pedigree data of Duroc (1586), Landrace (2256), and Yorkshire (3646) were analyzed. We estimated and compared various genomic and pedigree inbreeding coefficients using different models and approaches. A total of 709,384 ROH segments in Duroc, 816,898 in Landrace, and 1,401,781 in Yorkshire, with average lengths of 53.59 Mb, 56.21 Mb, and 53.46 Mb, respectively, were identified. Relatively, the Yorkshire breed had the shortest ROH segments, whereas the Landrace breed had the longest mean ROH segments. Sus scrofa chromosome 1 (SSC1) had the highest chromosomal coverage by ROH across all breeds. Across breeds, an absolute correlation (1.0) was seen between FROH total and FROH1-2Mb, showing that short ROH were the primary contributors to overall FROH values. The overall association between genomic and conventional inbreeding was weak, with values ranging from 0.058 to 0.140. In contrast, total genomic inbreeding (FROH) and ROH classes showed a strong association, ranging from 0.663 to 1.00, across the genotypes. The results of genomic and conventional inbreeding estimates improve our understanding of the genetic diversity among genotypes.

Whole-genome sequencing of two captive black soldier fly populations: Implications for commercial production

Black soldier fly (BSF; Hermetia illucens) is a promising insect species for food and feed production as its larvae can convert different organic waste to high-value protein. Selective breeding is one way to optimize production, but the potential of breeding is only starting to be explored and not yet utilized for BSF. To assist in monitoring a captive population and implementing a breeding program, genomics tools are imperative. We conducted whole genome sequencing of two captive populations separated by geographical distance - Denmark (DK) and Texas, USA (TX). Various population genetics analyses revealed a moderate genetic differentiation between two populations. Moreover, we observed higher inbreeding in the DK population, and the detection of a subpopulation within DK population aligned well with the recent foundation of the DK population from two captive populations. Additionally, we generated gene ontology annotation and variants annotation for wider potential applications. Our findings establish a robust marker set for research in population genetics, facilitating the monitoring of inbreeding and laying the groundwork for practical breeding programs for BSF.

Genetic diversity, population structure and origin of the native goats in Central Laos

Maintaining genetic diversity and variation in livestock populations is critical for natural and artificial selection promoting genetic improvement while avoiding problems due to inbreeding. In Laos, there are concerns that there has been a decline in genetic diversity and a rise in inbreeding among native goats in their village-based smallholder system. In this study, we investigated the genetic diversity of Lao native goats in Phin, Songkhone and Sepon districts in Central Laos for the first time using Illumina's Goat SNP50 BeadChip. We also explored the genetic relationships between Lao goats with 163 global goat populations from 36 countries. Our results revealled a close genetic relationship between Lao native goats and Chinese, Mongolian and Pakistani goats, sharing ancestries with Guangfen, Jining Grey and Luoping Yellow breeds (China) and Teddi goats (Pakistan). The observed (Ho) and expected (He) heterozygosity were 0.292 and 0.303 (Laos), 0.288 and 0.288 (Sepon), 0.299 and 0.308 (Phin) and 0.289 and 0.305 (Songkhone), respectively. There was low to moderate genetic differentiation (FST: 0.011-0.043) and negligible inbreeding coefficients (FIS: -0.001 to 0.052) between goat districts. The runs of homozygosity (ROH) had an average length of 5.92-6.85 Mb, with short ROH segments (1-5 Mb length) being the most prevalent (66.34%). Longer ROH segments (20-40 and >40 Mb length categories) were less common, comprising only 4.81% and 1.01%, respectively. Lao goats exhibit moderate genetic diversity, low-inbreeding levels and adequate effective population size. Some genetic distinctions between Lao goats may be explained by geographic and cultural features.

Genetic Diversity, Selection Signatures, and Genome-Wide Association Study Identify Candidate Genes Related to Litter Size in Hu Sheep

Hu sheep is a renowned prolific local sheep breed in China, widely distributed across the country due to its excellent reproductive performance. Deciphering the molecular mechanisms underlying the high fecundity of Hu sheep is crucial for improving the litter size of ewes. In this study, we genotyped 830 female Hu sheep using the Illumina OvineSNP50 BeadChip and performed genetic diversity analysis, selection signature detection, and a genome-wide association study (GWAS) for litter size. Our results revealed that the Hu sheep population exhibits relatively high genetic diversity. A total of 4927 runs of homozygosity (ROH) segments were detected, with the majority (74.73%) being short in length. Different genomic inbreeding coefficients (FROH, FHOM, FGRM, and FUNI) ranged from -0.0060 to 0.0126, showing low levels of inbreeding in this population. Additionally, we identified 91 candidate genomic regions through three complementary selection signature methods, including ROH, composite likelihood ratio (CLR), and integrated haplotype score (iHS), and annotated 189 protein-coding genes. Moreover, we observed two significant SNPs related to the litter size of Hu sheep using GWAS analysis based on a repeatability model. Integrating the selection signatures and the GWAS results, we identified 15 candidate genes associated with litter size, among which BMPR1B and UNC5C were particularly noteworthy. These findings provide valuable insights for improving the reproductive performance and breeding of high-fecundity lines of Hu sheep.

Genome-Wide Analysis of Genetic Diversity and Selection Signatures in Zaobei Beef Cattle

This investigation provides a comprehensive analysis of genomic diversity and selection signatures in Zaobei beef cattle, an indigenous breed known for its adaptation to hot and humid climates and superior meat quality. Whole-genome resequencing was conducted on 23 Zaobei cattle, compared with 46 Simmental cattle to highlight genetic distinctions. Population structure analysis confirmed the genetic uniqueness of Zaobei cattle. Using methods such as DASDC v1.01, XPEHH, and θπ ratio, we identified 230, 232, and 221 genes through DASDC, including hard sweeps, soft sweeps, and linkage sweeps, respectively. Coincidentally, 109 genes were identified when using XPEHH and θπ ratio methods. Together, these analyses revealed eight positive selection genes (ARHGAP15, ZNF618, USH2A, PDZRN4, SPATA6, ROR2, KCNIP3, and VWA3B), which are linked to critical traits such as heat stress adaptation, fertility, and meat quality. Moreover, functional enrichment analyses showed pathways related to autophagy, immune response, energy metabolism, and muscle development. The comprehensive genomic insights gained from this study provide valuable knowledge for breeding programs aimed at enhancing the beneficial traits in Zaobei cattle.

Genomic diversity and demographic history of the endangered Sichuan hill-partridge (Arborophila rufipectus)

Species conservation can be improved by knowledge of genetic diversity and demographic history. The Sichuan hill-partridge (Arborophila rufipectus, SP) is an endangered species endemic to the mountains in southwestern China. However, little is known about this species' genomic variation and demographic history. Here, we present a comprehensive whole-genome analysis of six SP individuals from the Laojunshan National Nature Reserve in Sichuan Province, China. We observe a relatively high genetic diversity and low level of recent inbreeding in the studied SP individuals. This suggests that the current population carries genetic variability that may benefit the long-term survival of this species, and that the present population may be larger than currently recognized. Analyses of demographic history showed that fluctuations in the effective population size of SP are inconsistent with changes of the historical climate. Strikingly, evidence from demographic modeling suggests SPs population decreased dramatically 15,100 years ago after the Last Glacial Maximum, possibly due to refugial isolation and later human interference. These results provide the first detailed and comprehensive genomic insights into genetic diversity, genomic inbreeding levels, and demographic history of the Sichuan hill-partridge, which are crucial for the conservation and management of this endangered species.

Analyzing Runs of Homozygosity Reveals Patterns of Selection in German Brown Cattle

An increasing trend in ancestral and classical inbreeding coefficients as well as inbreeding depression for longevity were found in the German Brown population. In addition, the proportion of US Brown Swiss genes is steadily increasing in German Browns. Therefore, the aim of the present study was to analyze the presence and genomic localization of runs of homozygosity (ROH) in order to evaluate their associations with the proportion of US Brown Swiss genes and survival rates of cows to higher lactations. Genotype data were sampled in 2364 German Browns from 258 herds. The final data set included 49,693 autosomal SNPs. We identified on average 35.996 ± 7.498 ROH per individual with a mean length of 8.323 ± 1.181 Mb. The genomic inbreeding coefficient FROH was 0.122 ± 0.032 and it decreased to 0.074, 0.031 and 0.006, when genomic homozygous segments > 8 Mb (FROH>8), >16 Mb (FROH>16) and >32 Mb (FROH>32) were considered. New inbreeding showed the highest correlation with FROH>32, whereas ancestral inbreeding coefficients had the lowest correlations with FROH>32. The correlation between the classical inbreeding coefficient and FROH was 0.572. We found significantly lower FROH, FROH>4, FROH>8 and FIS for US Brown Swiss proportions <60% compared to >80%. Cows surviving to the 2nd, 4th, 6th, 8th, and 10th lactation had lower genomic inbreeding for FROH and up to FROH>32, which was due to a lower number of ROH and a shorter average length of ROH. The strongest ROH island and consensus ROH shared by 50% of the animals was found on BTA 6 at 85-88 Mb. The genes located in this genomic region were associated with longevity (NPFFR2 and ADAMTS3), udder health and morphology (SLC4A4, NPFFR2, GC and RASSF6), milk production, milk protein percentage, coagulation properties of milk and milking speed (CSN3). On BTA 2, a ROH island was detected only in animals with <60% US Brown Swiss genes. Genes within this region are predominantly important for dual-purpose cattle breeds including Original Browns. For cows reaching more than 9 lactations, an exclusive ROH island was identified on BTA 7 with genes assumed to be associated with longevity. The analysis indicated that genomic homozygous regions important for Original Browns are still present and also ROH containing genes affecting longevity may have been identified. The breeding of German Browns should prevent any further increase in genomic inbreeding and run a breeding program with balanced weights on production, robustness and longevity.

Genetic diversity and signatures of selection in Icelandic horses and Exmoor ponies

BACKGROUND

The Icelandic horse and Exmoor pony are ancient, native breeds, adapted to harsh environmental conditions and they have both undergone severe historic bottlenecks. However, in modern days, the selection pressures on these breeds differ substantially. The aim of this study was to assess genetic diversity in both breeds through expected (HE) and observed heterozygosity (HO) and effective population size (Ne). Furthermore, we aimed to identify runs of homozygosity (ROH) to estimate and compare genomic inbreeding and signatures of selection in the breeds.

RESULTS

HO was estimated at 0.34 and 0.33 in the Icelandic horse and Exmoor pony, respectively, aligning closely with HE of 0.34 for both breeds. Based on genomic data, the Ne for the last generation was calculated to be 125 individuals for Icelandic horses and 42 for Exmoor ponies. Genomic inbreeding coefficient (FROH) ranged from 0.08 to 0.20 for the Icelandic horse and 0.12 to 0.27 for the Exmoor pony, with the majority of inbreeding attributed to short ROHs in both breeds. Several ROH islands associated with performance were identified in the Icelandic horse, featuring target genes such as DMRT3, DOCK8, EDNRB, SLAIN1, and NEURL1. Shared ROH islands between both breeds were linked to metabolic processes (FOXO1), body size, and the immune system (CYRIB), while private ROH islands in Exmoor ponies were associated with coat colours (ASIP, TBX3, OCA2), immune system (LYG1, LYG2), and fertility (TEX14, SPO11, ADAM20).

CONCLUSIONS

Evaluations of genetic diversity and inbreeding reveal insights into the evolutionary trajectories of both breeds, highlighting the consequences of population bottlenecks. While the genetic diversity in the Icelandic horse is acceptable, a critically low genetic diversity was estimated for the Exmoor pony, which requires further validation. Identified signatures of selection highlight the differences in the use of the two breeds as well as their adaptive trait similarities. The results provide insight into genomic regions under selection pressure in a gaited performance horse breed and various adaptive traits in small-sized native horse breeds. This understanding contributes to preserving genetic diversity and population health in these equine populations.

Runs of homozygosity reveal contrasting histories of inbreeding across global lineages of the edible porcini mushroom, Boletus edulis

Inbreeding, the mating of individuals that are related through common ancestry, is of central importance in evolutionary and conservation biology due to its impacts on individual fitness and population dynamics. However, while advanced genomic approaches have revolutionised the study of inbreeding in animals, genomic studies of inbreeding are rare in plants and lacking in fungi. We investigated global patterns of inbreeding in the prized edible porcini mushroom Boletus edulis using 225 whole genomes from seven lineages distributed across the northern hemisphere. Genomic inbreeding was quantified using runs of homozygosity (ROHs). We found appreciable variation both among and within lineages, with some individuals having over 20% of their genomes in ROHs. Much of this variation could be explained by a combination of elevation and latitude, and to a lesser extent by predicted habitat suitability during the last glacial maximum. In line with this, the majority of ROHs were short, reflecting ancient common ancestry dating back approximately 200-1700 generations ago, while longer ROHs indicative of recent common ancestry (less than approximately 50 generations ago) were infrequent. Our study reveals the inbreeding legacy of major climatic events in a widely distributed forest mutualist, aligning with prevailing theories and empirical studies of the impacts of historical glaciation events on the dominant forest tree species of the northern hemisphere.

Genome-wide detection of runs of homozygosity and heterozygosity in Tunchang pigs

Tunchang pigs, mainly distributed throughout Hainan Province of China, are well-known for their superior meat quality, crude feed tolerance, and adaptability to high temperatures and humidity. Runs of homozygosity (ROH) can provide valuable information about the inbreeding coefficient in individuals and selection signals that may reveal candidate genes associated with key functional traits. Runs of heterozygosity (ROHet) are commonly associated with balance selection, which can help us understand the adaptive evolutionary history of domestic animals. In this study, we investigated ROHs and ROHets in 88 Tunchang pigs. We also compared the estimates of inbreeding coefficients in individuals calculated based on four methods. In summary, we detected a total of 16 ROH islands in our study, and 100 genes were found within ROH regions. These genes were correlated with economically important traits such as reproduction (e.g., SERPIND1, HIRA), meat quality (e.g., PI4KA, TBX1), immunity (e.g., ESS2, RANBP1), adaption to heat stress (TXNRD2 and DGCR8), and crude food tolerance (TRPM6). Moreover, we discovered 18 ROHet islands harbouring genes associated with reproduction (e.g., ARHGEF12, BMPR2), immune system (e.g., BRD4, DNMT3B). These findings may help us design effective breeding and conservation strategies for this unique breed.

Genomic analysis of inbreeding and coancestry in Nordic Jersey and Holstein dairy cattle populations

In recent years, genomic selection (GS) has accelerated genetic gain in dairy cattle breeds worldwide. Despite the evident genetic progress, several dairy populations have also encountered challenges such as heightened inbreeding rates and reduced effective population sizes. The challenge has been to find a balance between achieving substantial genetic gain while managing genetic diversity within the population, thereby mitigating the negative effects of inbreeding depression. This study aims to elucidate the impact of GS on pedigree and genomic rates of inbreeding (ΔF) and coancestry (ΔC) in Nordic Jersey (NJ) and Holstein (NH) cattle populations. Furthermore, key genetic metrics, including the generation interval (L), effective population size (Ne), and future effective population size (FNe) were assessed between 2 time periods, before and after GS, and across distinct animal cohorts in both breeds: females, bulls, and approved semen-producing bulls (AI-sires). Analysis of ΔF and ΔC revealed distinct trends across the studied periods and animal groups. Notably, there was a consistent increase in yearly ΔF for most animal groups in both breeds. An exception was observed in NH AI-sires, which demonstrated a slight decrease in yearly ΔF. Moreover, NJ displayed minimal changes in yearly ΔC between the periods, whereas NH exhibited elevated ΔC values across all animal groups. Particularly striking was the substantial increase in yearly ΔC within the NH female population, surging from 0.02% to 0.39% between the periods. Implementation of GS resulted in a reduction of the generation interval across all animal cohorts in both NJ and NH breeds. However, the extent of reduction was more pronounced in males compared with females. This reduction in generation interval influenced generational changes in ΔF and ΔC. Bulls and AI-sires of both breeds exhibited reduced generational ΔF between periods, in contrast to females that demonstrated an opposing pattern. Between the periods, NJ maintained a relatively stable Ne (29.4 before and 30.3 after GS), whereas NH experienced a notable decline from 54.3 to 42.8. Female groups in both breeds displayed a negative Ne trend, whereas males demonstrated either neutral or positive Ne developments. Regarding FNe, NJ exhibited positive FNe development with an increase from 40.7 to 57.2. The opposite was observed in NH, where FNe decreased from 198.8 to 42.7. In summary, it was evident that the genomic methods could detect differences between the populations and changes in ΔF and ΔC more efficiently than pedigree methods. Implementation of GS yielded positive outcomes within the NJ population regarding the rate of coancestry but the opposite was observed with NH. Moreover, analysis of ΔC data hints at the potential to decrease future ΔF through informed mating strategies. Conversely, NH faces more pressing concerns, even though ΔF remains comparatively modest in contrast to what has been observed in other Holstein populations. These findings underscore the necessity of genomic control of inbreeding and coancestry with strategic changes in the Nordic breeding schemes for dairy to ensure long-term sustainability in the forthcoming years.

Characterisation of runs of homozygosity and inbreeding coefficients in the red-brown Korean native chickens

OBJECTIVE

The analysis of runs of homozygosity (ROH) has been applied to assess the level of inbreeding and identify selection signatures in various livestock species. The objectives of this study were to characterize the ROH pattern, estimate the rate of inbreeding, and identify signatures of selection in the red-brown Korean native chickens.

METHODS

The Illumina 60K single nucleotide polymorphism chip data of 651 chickens was used in the analysis. Runs of homozygosity were analysed using the PLINK v1.9 software. Inbreeding coefficients were estimated using the GCTA software and their correlations were examined. Genomic regions with high levels of ROH were explored to identify selection signatures.

RESULTS

A total of 32,176 ROH segments were detected in this study. The majority of the ROH segments were shorter than 4 Mb. The average ROH inbreeding coefficients (FROH) varied with the length of ROH segments. The means of inbreeding coefficients calculated from different methods were also variable. The correlations between different inbreeding coefficients were positive and highly variable (r = 0.18-1). Five ROH islands harbouring important quantitative trait loci were identified.

CONCLUSION

This study assessed the level of inbreeding and patterns of homozygosity in Red-brown native Korean chickens. The results of this study suggest that the level of recent inbreeding is low which indicates substantial progress in the conservation of red-brown Korean native chickens. Additionally, Candidate genomic regions associated with important production traits were detected in homozygous regions.

Genetic analysis of a Kaijiang duck conservation population through genome-wide scan

1. The Kaijiang duck is a native Chinese breed known for its excellent egg laying performance, killing-out percentage (88.57%), and disease resistance. The assessment of population genetic structure is the basis for understanding the genetics of indigenous breeds and for their protection and management.2. In this study, whole-genome sequencing was performed on 60 Kaijiang ducks to identify genetic variations and investigate the population structure. Homozygosity (ROH) analysis was conducted to assess inbreeding levels in the population.3. The study revealed a moderate level of inbreeding, indicated by an average inbreeding coefficient of 0.1043. This may impact the overall genetic diversity.4. Genomic Regions of Interest identified included 168 genomic regions exhibiting high levels of autozygosity. These regions were associated with processes including muscle growth, pigmentation, neuromodulation, and growth and reproduction.5. The significance of these pathways indicated their potential role in shaping the desirable traits of the Kaijiang duck. These findings provide insights into the genetic basis of the Kaijiang duck's desirable traits and can inform future breeding and conservation efforts.

Assessing different metrics of pedigree and genomic inbreeding and inbreeding effect on growth, fertility, and feed efficiency traits in a closed-herd Nellore cattle population

BACKGROUND

The selection of individuals based on their predicted breeding values and mating of related individuals can increase the proportion of identical-by-descent alleles. In this context, the objectives of this study were to estimate inbreeding coefficients based on alternative metrics and data sources such as pedigree (FPED), hybrid genomic relationship matrix H (FH), and ROH of different length (FROH); and calculate Pearson correlations between the different metrics in a closed Nellore cattle population selected for body weight adjusted to 378 days of age (W378). In addition to total FROH (all classes) coefficients were also estimated based on the size class of the ROH segments: FROH1 (1-2 Mb), FROH2 (2-4 Mb), FROH3 (4-8 Mb), FROH4 (8-16 Mb), and FROH5 (> 16 Mb), and for each chromosome (FROH_CHR). Furthermore, we assessed the effect of each inbreeding metric on birth weight (BW), body weights adjusted to 210 (W210) and W378, scrotal circumference (SC), and residual feed intake (RFI). We also evaluated the chromosome-specific effects of inbreeding on growth traits.

RESULTS

The correlation between FPED and FROH was 0.60 while between FH and FROH and FH and FPED were 0.69 and 0.61, respectively. The annual rate of inbreeding was 0.16% for FPED, 0.02% for FH, and 0.16% for FROH. A 1% increase in FROH5 resulted in a reduction of up to -1.327 ± 0.495 kg in W210 and W378. Four inbreeding coefficients (FPED, FH, FROH2, and FROH5) had a significant effect on W378, with reductions of up to -3.810 ± 1.753 kg per 1% increase in FROH2. There was an unfavorable effect of FPED on RFI (0.01 ± 0.0002 kg dry matter/day) and of FROH on SC (-0.056 ± 0.022 cm). The FROH_CHR coefficients calculated for BTA3, BTA5, and BTA8 significantly affected the growth traits.

CONCLUSIONS

Inbreeding depression was observed for all traits evaluated. However, these effects were greater for the criterion used for selection of the animals (i.e., W378). The increase in the genomic inbreeding was associated with a higher inbreeding depression on the traits evaluated when compared to pedigree-based inbreeding. Genomic information should be used as a tool during mating to optimize control of inbreeding and, consequently, minimize inbreeding depression in Nellore cattle.

Identification of Heilongjiang crossbred beef cattle pedigrees and reveals functional genes related to economic traits based on whole-genome SNP data

Introduction: To enhance the beef cattle industry, Heilongjiang Province has developed a new Crossbred beef cattle variety through crossbreeding with exotic commercial breeds. This new variety exhibits relatively excellent meat quality, and efficient reproductive performance, catering to market demands. Method: This study employed whole genome resequencing technology to analyze the genetic pedigree and diversity of 19 Heilongjiang Crossbred beef cattle, alongside 59 published genomes from East Asian, Eurasian, and European taurine cattle as controls. In addition, genes related to production traits were also searched by identifying Runs of Homozygosity (ROH) islands and important fragments from ancestors. Results: A total of 14,427,729 biallelic SNPs were discovered, with the majority located in intergenic and intron regions and a small percentage in exon regions, impacting protein function. Population genetic analyses including Principal Component Analysis (PCA), Neighbor-Joining (NJ) tree, and ADMIXTURE identified Angus, Holstein, and Mishima as the main ancestors of Crossbred beef cattle. In genetic diversity analysis, nucleotide diversity, linkage disequilibrium, and inbreeding coefficient analysis reveal that the genetic diversity of Crossbred beef cattle is at a moderate level, and a higher inbreeding coefficient indicates the need for careful breeding management. In addition, some genes related to economic traits are identified through the identification of Runs of Homozygosity (ROH) islands and important fragments from ancestors. Conclusion: This comprehensive genomic characterization supports the targeted improvement of economically important traits in Crossbred beef cattle, facilitating advanced breeding strategies.

Genomic insights into adaptation and inbreeding among Sub-Saharan African cattle from pastoral and agropastoral systems

Background

In Sub-Saharan Africa (SSA), cattle are crucial for socioeconomic stability yet face numerous environmental stressors such as diseases, parasites, and extreme heat within pastoral and agropastoral systems. Despite their significance, gaps remain in understanding how genetic diversity and inbreeding influence traits essential for disease resistance and environmental adaptability. This study examines the genomic adaptations that enable SSA cattle to thrive under these conditions and assesses the impact of inbreeding on such adaptive traits.

Methods

We analyzed genomic data from 113 cattle across four breeds-Kuri, N'dama, Zebu-Fulani, and Zebu-Bororo-employing Runs of Homozygosity (ROH) and Integrated Haplotype Score (iHS) analyses to identify historical and recent genetic selections. Strict quality controls using PLINK software ensured accurate genomic pattern identification related to adaptation and inbreeding.

Results

ROH analysis revealed islands with genes such as RSAD2, CMPK2, and NOTCH1, which are involved in immune response and cellular stress management, highlighting regions of historical selection that have likely provided adaptive advantages in overcoming environmental and pathogenic stresses. In contrast, iHS analysis identified genes under recent selection like HIPK1, involved in stress response regulation, and EPHA5, which plays a crucial role in neural development and synaptic functions, potentially equipping these breeds with novel adaptations to ongoing and emergent environmental challenges.

Conclusion

This research confirms that selective pressures inherent in pastoral and agropastoral systems profoundly influence the genetic structure of SSA cattle. By delineating the genetic bases of key adaptive traits, our study offers crucial insights for targeted breeding programs to enhance cattle resilience and productivity. These findings provide a valuable framework for future genetic improvements and conservation strategies, crucial for sustainable livestock management and economic stability in SSA.

Determinants of Human Asymmetry: Does Asymmetrical Retinal Vasculature Predict Asymmetry Elsewhere in the Body?

The aim of this study was to explore retinal vasculature asymmetry (ReVA) patterns in subjects from the islands of Vis and Korcula and the city of Split, Croatia. Asymmetry estimates were based on topographic image analysis of non-mydriatic retinal fundus photographs and compared with nine ophthalmic measurements, three Doppler-based pressure indices and eight frequencies of audiometry. ReVA was also correlated to the genomic runs of homozygosity (ROHs) and used in a Cox regression survival model, where we adjusted for the effects of sex, age and comorbidity. In 1873 subjects, ReVA estimates were significantly correlated with most ophthalmic asymmetry measures, less strongly with the ankle-brachial pressure index and only modestly with higher-amplitude audiometry asymmetries (lowest p = 0.020). ReVA was significantly correlated with the number of ROHs (r = 0.229, p < 0.001) but less strongly with the ROH length (r = 0.101, p < 0.001). The overlap of asymmetries was low, with only 107 subjects (5.7% of the total sample) who had two or more instances in which they were among the top 10%. Multiple asymmetries did not affect survival (HR = 0.74, 95% confidence intervals 0.45-1.22). Retinal vasculature asymmetry is a poor predictor of asymmetry elsewhere in the body. Despite its existence and apparent association with comorbidities, the observed extent of retinal vasculature asymmetry did not affect the lifespan in this population.

Genome-Wide Association Studies of Growth Trait Heterosis in Crossbred Meat Rabbits

The application of heterosis can not only effectively improve the disease resistance and meat quality of livestock, but also significantly enhance the reproduction and growth of livestock and poultry. We conducted genome-wide association studies using data from F2 crossbred meat rabbits to screen out candidate genes with significant dominant effects associated with economic trait variation. High-throughput sequencing technology was used to obtain SNPs covering the whole genome to evaluate the homozygosity of the population genome, and analyze the number, length, frequency, and distribution of ROHs in the population. Candidate genes related to economic traits of meat rabbits were searched based on high-frequency ROH regions. After quality control filtering of genotype data, 380 F2 crossbred rabbits were identified with 78,579 SNPs and 42,018 ROHs on the autosomes. The fitting of the Logistic growth curve model showed that 49-day-old rabbits were a growth inflection point. Then, through genome-wide association studies, 10 SNP loci and seven growth trait candidate genes were found to be significantly related to body weight in meat rabbits at 84 days of age. In addition, we revealed the functional roles and locations of 20 candidate genes in the high-frequency ROH region associated with economic traits in meat rabbits. This study identified potential genes associated with growth and development in the high-frequency ROH region of meat rabbits. In this study, the identified candidate genes can be used as molecular markers for assisted selection in meat rabbits. At the same time, the inbreeding situation based on ROH assessment can provide reference for breeding and breeding preservation of meat rabbits.

Insights into the genomic homogeneity of Moroccan indigenous sheep breeds though the lens of runs of homozygosity

Numerous studies have indicated that Morocco's indigenous sheep breeds are genetically homogenous, posing a risk to their survival in the challenging harsh climate conditions where they predominantly inhabit. To understand the genetic behind genetic homogeneity through the lens of runs of homozygosity (ROH), we analyzed the whole genome sequences of five indigenous sheep breeds (Beni Guil, Ouled Djellal, D'man, Sardi, Timahdite and Admixed).The results from principal component, admixture, Fst, and neighbour joining tree analyses consistently showed a homogenous genetic structure. This structure was characterized by an average length of 1.83 Mb for runs of homozygosity (ROH) segments, with a limited number of long ROH segments (24-48 Mb and > 48 Mb). The most common ROH segments were those ranging from 1-6 Mb. The most significant regions of homozygosity (ROH Islands) were mostly observed in two chromosomes, namely Chr1 and Chr5. Specifically, ROH Islands were exclusively discovered in the Ouled Djellal breed on Chr1, whereas Chr5 exhibited ROH Islands in all breeds. The analysis of ROH Island and iHS technique was employed to detect signatures of selection on Chr1 and Chr5. The results indicate that Chr5 had a high level of homogeneity, with the same genes being discovered across all breeds. In contrast, Chr1 displays some genetic variances between breeds. Genes identified on Chr5 included SLC39A1, IL23A, CAST, IL5, IL13, and IL4 which are responsible for immune response while genes identified on Chr1 include SOD1, SLAMF9, RTP4, CLDN1, and PRKAA2. ROH segment profile and effective population sizes patterns suggests that the genetic uniformity of studied breeds is the outcome of events that transpired between 250 and 300 generations ago. This research not only contributes to the understanding of ROH distribution across breeds but helps design and implement native sheep breeding and conservation strategies in Morocco. Future research, incorporating a broader sample size and utilizing the pangenome for reference, is recommended to further elucidate these breeds' genomic landscapes and adaptive mechanisms.

Genetic diversity analysis of Inner Mongolia cashmere goats (Erlangshan subtype) based on whole genome re-sequencing

BACKGROUND

Inner Mongolia cashmere goat (IMCG), renowned for its superior cashmere quality, is a Chinese indigenous goat breed that has been developed through natural and artificial selection over a long period. However, recently, the genetic resources of IMCGs have been significantly threatened by the introduction of cosmopolitan goat breeds and the absence of adequate breed protection systems.

RESULTS

In order to assess the conservation effectiveness of IMCGs and efficiently preserve and utilize the purebred germplasm resources, this study analyzed the genetic diversity, kinship, family structure, and inbreeding of IMCGs utilizing resequencing data from 225 randomly selected individuals analyzed using the Plink (v.1.90), GCTA (v.1.94.1), and R (v.4.2.1) software. A total of 12,700,178 high-quality SNPs were selected through quality control from 34,248,064 SNP sites obtained from 225 individuals. The average minor allele frequency (MAF), polymorphic information content (PIC), and Shannon information index (SHI) were 0.253, 0.284, and 0.530, respectively. The average observed heterozygosity (Ho) and the average expected heterozygosity (He) were 0.355 and 0.351, respectively. The analysis of the identity by state distance matrix and genomic relationship matrix has shown that most individuals' genetic distance and genetic relationship are far away, and the inbreeding coefficient is low. The family structure analysis identified 10 families among the 23 rams. A total of 14,109 runs of homozygosity (ROH) were identified in the 225 individuals, with an average ROH length of 1014.547 kb. The average inbreeding coefficient, calculated from ROH, was 0.026 for the overall population and 0.027 specifically among the 23 rams, indicating a low level of inbreeding within the conserved population.

CONCLUSIONS

The IMCGs exhibited moderate polymorphism and a low level of kinship with inbreeding occurring among a limited number of individuals. Simultaneously, it is necessary to prevent the loss of bloodline to guarantee the perpetuation of the IMCGs' germplasm resources.

Temporal dynamics of woolly mammoth genome erosion prior to extinction

A number of species have recently recovered from near-extinction. Although these species have avoided the immediate extinction threat, their long-term viability remains precarious due to the potential genetic consequences of population declines, which are poorly understood on a timescale beyond a few generations. Woolly mammoths (Mammuthus primigenius) became isolated on Wrangel Island around 10,000 years ago and persisted for over 200 generations before becoming extinct around 4,000 years ago. To study the evolutionary processes leading up to the mammoths' extinction, we analyzed 21 Siberian woolly mammoth genomes. Our results show that the population recovered quickly from a severe bottleneck and remained demographically stable during the ensuing six millennia. We find that mildly deleterious mutations gradually accumulated, whereas highly deleterious mutations were purged, suggesting ongoing inbreeding depression that lasted for hundreds of generations. The time-lag between demographic and genetic recovery has wide-ranging implications for conservation management of recently bottlenecked populations.

Using high-density SNP data to unravel the origin of the Franches-Montagnes horse breed

BACKGROUND

The Franches-Montagnes (FM) is the last native horse breed of Switzerland, established at the end of the 19th century by cross-breeding local mares with Anglo-Norman stallions. We collected high-density SNP genotype data (Axiom™ 670 K Equine genotyping array) from 522 FM horses, including 44 old-type horses (OF), 514 European Warmblood horses (WB) from Sweden and Switzerland (including a stallion used for cross-breeding in 1990), 136 purebred Arabians (AR), 32 Shagya Arabians (SA), and 64 Thoroughbred (TB) horses, as introgressed WB stallions showed TB origin in their pedigrees. The aim of the study was to ascertain fine-scale population structures of the FM breed, including estimation of individual admixture levels and genomic inbreeding (FROH) by means of Runs of Homozygosity.

RESULTS

To assess fine-scale population structures within the FM breed, we applied a three-step approach, which combined admixture, genetic contribution, and FROH of individuals into a high-resolution network visualization. Based on this approach, we were able to demonstrate that population substructures, as detected by model-based clustering, can be either associated with a different genetic origin or with the progeny of most influential sires. Within the FM breed, admixed horses explained most of the genetic variance of the current breeding population, while OF horses only accounted for a small proportion of the variance. Furthermore, we illustrated that FM horses showed high TB admixture levels and we identified inconsistencies in the origin of FM horses descending from the Arabian stallion Doktryner. With the exception of WB, FM horses were less inbred compared to the other breeds. However, the relatively few but long ROH segments suggested diversity loss in both FM subpopulations. Genes located in FM- and OF-specific ROH islands had known functions involved in conformation and behaviour, two traits that are highly valued by breeders.

CONCLUSIONS

The FM remains the last native Swiss breed, clearly distinguishable from other historically introgressed breeds, but it suffered bottlenecks due to intensive selection of stallions, restrictive mating choices based on arbitrary definitions of pure breeding, and selection of rare coat colours. To preserve the genetic diversity of FM horses, future conservation managements strategies should involve a well-balanced selection of stallions (e.g., by integrating OF stallions in the FM breeding population) and avoid selection for rare coat colours.

Patterns of reproduction and autozygosity distinguish the breeding from nonbreeding gray wolves of Yellowstone National Park

For species of management concern, accurate estimates of inbreeding and associated consequences on reproduction are crucial for predicting their future viability. However, few studies have partitioned this aspect of genetic viability with respect to reproduction in a group-living social mammal. We investigated the contributions of foundation stock lineages, putative fitness consequences of inbreeding, and genetic diversity of the breeding versus nonreproductive segment of the Yellowstone National Park gray wolf population. Our dataset spans 25 years and seven generations since reintroduction, encompassing 152 nuclear families and 329 litters. We found more than 87% of the pedigree foundation genomes persisted and report influxes of allelic diversity from two translocated wolves from a divergent source in Montana. As expected for group-living species, mean kinship significantly increased over time but with minimal loss of observed heterozygosity. Strikingly, the reproductive portion of the population carried a significantly lower genome-wide inbreeding coefficients, autozygosity, and more rapid decay for linkage disequilibrium relative to the nonbreeding population. Breeding wolves had significantly longer lifespans and lower inbreeding coefficients than nonbreeding wolves. Our model revealed that the number of litters was negatively significantly associated with heterozygosity (R = -0.11). Our findings highlight genetic contributions to fitness, and the importance of the reproductively active individuals in a population to counteract loss of genetic variation in a wild, free-ranging social carnivore. It is crucial for managers to mitigate factors that significantly reduce effective population size and genetic connectivity, which supports the dispersion of genetic variation that aids in rapid evolutionary responses to environmental challenges.

Reproductive traits in Pura Raza Española mares manifest inbreeding depression from low levels of homozygosity

Inbreeding depression is a genetic phenomenon associated with the loss of fitness and mean phenotypic performance due to mating between relatives. Historically, inbreeding coefficients have been estimated from pedigree information. However, the onset of genomic selection programs provides large datasets of individuals genotyped using SNP arrays, enabling more precise assessment of an individual's genomic-level inbreeding using genomic data. One of the traits most sensitive to issues stemming from increased inbreeding is reproduction. This is particularly important in equine, in which fertility is only moderate compared to other livestock species. To explore this further, we evaluated the effect of inbreeding on five reproductive traits (age at first foaling (AFF), average interval between foalings (AIF), total number of foalings (NF), productive life (PL) and reproductive efficiency (RE)) in Pura Raza Español mares using genomic data. Residual predicted phenotypes were obtained by purging these traits through the REML (wgResidual) and ssGREML (gResidual) approaches in reproductive data of 29,847 PRE mares using the BLUPF90+ program. Next, we used pedigree-based (Fped) and ROH-based genomic (FROH) inbreeding coefficients derived from 1018 animals genotyped with 61,271 SNPs to estimate the inbreeding depression (linear regression). Our results indicated significant levels of inbreeding depression for all reproductive traits, with the exception of the AIF trait when Fped was used. However, all traits were negatively affected by the increase in genomic inbreeding, and FROH was found to capture more inbreeding depression than Fped. Likewise, REML models (ssGREML) using genomic data for estimated predicted residual phenotypes resulted in higher variance explained by the model compared with the models not using genomics (REML). Finally, a segmented regression analysis was conducted to evaluate the effect of inbreeding depression, revealing that the levels of genealogical and genomic homozygosity do not manifest uniformly in reproductive traits. In contrast, the levels of inbreeding depression ranged from low to high as homozygosity increased. This analysis also showed that reproductive traits are very sensitive to inbreeding depression, even with relatively low levels of homozygosity.

Effects of inbreeding on reproductive success in endangered North Atlantic right whales

Only approximately 356 North Atlantic right whales (Eubalaena glacialis) remain. With extremely low levels of genetic diversity, limited options for mates, and variation in reproductive success across females, there is concern regarding the potential for genetic limitations of population growth from inbreeding depression. In this study, we quantified reproductive success of female North Atlantic right whales with a modified de-lifing approach using reproductive history information collected over decades of field observations. We used double-digest restriction site-associated sequencing to sequence approximately 2% of the genome of 105 female North Atlantic right whales and combined genomic inbreeding estimates with individual fecundity values to assess evidence of inbreeding depression. Inbreeding depression could not explain the variance in reproductive success of females, however we present evidence that inbreeding depression may be affecting the viability of inbred fetuses-potentially lowering the reproductive success of the species as a whole. Combined, these results allay some concerns that genetic factors are impacting species survival as genetic diversity is being retained through selection against inbred fetuses. While still far fewer calves are being born each year than expected, the small role of genetics underlying variance in female fecundity suggests that variance may be explained by external factors that can potentially be mitigated through protection measures designed to reduce serious injury and mortality from human activities.

Inbreeding depression and runs of homozygosity islands in Asturiana de los Valles cattle breed after 30 years of selection

Inbreeding depression results in a decrease in the average phenotypic values of affected traits. It has been traditionally estimated from pedigree-based inbreeding coefficients. However, with the development of single-nucleotide polymorphism arrays, novel methods were developed for calculating the inbreeding coefficient, and consequently, inbreeding depression. The aim of the study was to analyse inbreeding depression in 6 growth and 2 reproductive traits in the Asturiana de los Valles cattle breed using both genealogical and molecular information. The pedigree group comprised 225,848 records and an average equivalent number of complete generations of 2.3. The molecular data comprised genotypes of 2693 animals using the Affymetrix medium-density chip. Using the pedigree information, three different inbreeding coefficients were estimated for the genotyped animals: the full pedigree coefficient (FPED), and the recent and ancient inbreeding coefficients based on the information of the last three generations (FPED<3G) and until the last three generations (FPED>3G), respectively. Using the molecular data, seven inbreeding coefficients were calculated. Four of them were estimated based on runs of homozygosity (ROH), considering (1) the total length (FROH), (2) segments shorter than 4 megabases (FROH<4), (3) between 4 and 17 megabases (FROH4-17), and (4) longer than 17 Mb (FROH>17). Additionally, the three inbreeding coefficients implemented in the Plink software (FHAT1-3) were estimated. Inbreeding depression was estimated using linear mixed-effects model with inbreeding coefficients used as covariates. All analysed traits (birth weight, preweaning average daily gain, weaning weight adjusted at 180 days, carcass weight, calving ease, age at first calving, calving interval) showed a statistically significant non-zero effect of inbreeding depression estimated from the pedigree group, except for the Postweaning Average Daily Gain trait. When inbreeding coefficients were based on the genomic group, statistically significant inbreeding depression was observed for two traits, Preweaning Average Daily Gain and Weaning Weight based on FROH, FROH>17, and FHAT3 inbreeding coefficients. Nevertheless, similar to inbreeding depression estimated based on pedigree information, estimates of inbreeding depression based on genomic information had no relevant economic impact. Despite this, from a long-term perspective, genotyped data could be included to maximize genetic progress in genetic programs following an optimal genetic contribution strategy and to consider individual inbreeding load instead global inbreeding. ROH islands were identified on chromosomes 2, 3, 8, 10, and 16. Such regions contain several candidate genes for growth development, intramuscular fat, body weight and lipid metabolism that are related to production traits selected in Asturiana de los Valles breed.

Impact of inbreeding on production, fertility, and health traits in German Holstein dairy cattle utilizing various inbreeding estimators

In dairy cattle production, it is important to understand how inbreeding affects production, fertility, and health traits. However, there is still limited use of genomic information to estimate inbreeding, despite advancements in genotyping technologies. To address this gap, we investigated the effect of inbreeding on German Holstein dairy cattle using both pedigree-based and genomic-based inbreeding estimators. We employed one method based on pedigree information (Fped) together with 6 genomic-based methods, including 3 genome-wide complex trait analysis software estimators (Fhat1, Fhat2, Fhat3), VanRaden's first method (FVR1, with observed allele frequencies, and FVR0.5, when allele frequencies are set to 0.5), and one based on runs of homozygosity (Froh). Data from 24,489 cows with both phenotypes and genotypes were used, with a pedigree including 232,780 animals born between 1970 and 2018. We analyzed the effects of inbreeding depression on production, fertility, and health traits separately, using single-trait linear animal models as well as threshold models to account for the binary nature of the health traits. For the health traits, we transformed solutions from the liability scale to a probability scale for easier interpretation. Our results showed that the mean inbreeding coefficients from all estimators ranged from -0.003 to 0.243, with negative values observed for most genomic-based methods. We found out that a 1% increase in inbreeding caused a depression ranging from 25.94 kg (Fhat1) to 40.62 kg (Fhat3), 1.18 kg (Fhat2) to 1.70 kg (Fhat3), 0.90 kg (Fhat2) to 1.45 kg (Froh and Fhat3), 0.19 (Fped) to 0.34 d (Fhat3) for 305-d milk yield, fat, protein, and calving interval, respectively. The health traits showed very slight gradual changes when inbreeding was increased steadily from 0% to 50%, with digital dermatitis showing a rather contrasting trend to that of mastitis, which increased the more an animal was inbred. Overall, our study highlights the importance of considering both pedigree-based and genomic-based inbreeding estimators when assessing the impact on inbreeding, emphasizing that not all inbreeding is harmful.

Island demographics and trait associations in white-tailed deer

When a population is isolated and composed of few individuals, genetic drift is the paramount evolutionary force and results in the loss of genetic diversity. Inbreeding might also occur, resulting in genomic regions that are identical by descent, manifesting as runs of homozygosity (ROHs) and the expression of recessive traits. Likewise, the genes underlying traits of interest can be revealed by comparing fixed SNPs and divergent haplotypes between affected and unaffected individuals. Populations of white-tailed deer (Odocoileus virginianus) on islands of Saint Pierre and Miquelon (SPM, France) have high incidences of leucism and malocclusions, both considered genetic defects; on the Florida Keys islands (USA) deer exhibit smaller body sizes, a polygenic trait. Here we aimed to reconstruct island demography and identify the genes associated with these traits in a pseudo case-control design. The two island populations showed reduced levels of genomic diversity and a build-up of deleterious mutations compared to mainland deer; there was also significant genome-wide divergence in Key deer. Key deer showed higher inbreeding levels, but not longer ROHs, consistent with long-term isolation. We identified multiple trait-related genes in ROHs including LAMTOR2 which has links to pigmentation changes, and NPVF which is linked to craniofacial abnormalities. Our mixed approach of linking ROHs, fixed SNPs and haplotypes matched a high number (~50) of a-priori body size candidate genes in Key deer. This suite of biomarkers and candidate genes should prove useful for population monitoring, noting all three phenotypes show patterns consistent with a complex trait and non-Mendelian inheritance.

Does inbreeding contribute to pregnancy loss in Thoroughbred horses?

BACKGROUND

Excessive inbreeding increases the probability of uncovering homozygous recessive genotypes and has been associated with an increased risk of retained placenta and lower semen quality. No genomic analysis has investigated the association between inbreeding levels and pregnancy loss.

OBJECTIVES

To compare genetic inbreeding coefficients (F) of naturally occurring Thoroughbred Early Pregnancy Loss (EPLs), Mid and Late term Pregnancy Loss (MLPL) and Controls. The F value was hypothesised to be higher in cases of pregnancy loss (EPLs and MLPLs) than Controls.

STUDY DESIGN

Observational case-control study.

METHODS

Allantochorion and fetal DNA from EPL (n = 37, gestation age 14-65 days), MLPL (n = 94, gestational age 70 days-24 h post parturition) and Controls (n = 58) were genotyped on the Axiom Equine 670K SNP Genotyping Array. Inbreeding coefficients using Runs of Homozygosity (FROH) were calculated using PLINK software. ROHs were split into size categories to investigate the recency of inbreeding.

RESULTS

MLPLs had significantly higher median number of ROH (188 interquartile range [IQR], 180.8-197.3), length of ROH (3.10, IQR 2.93-3.33), and total number of ROH (590.8, IQR 537.3-632.3), and FROH (0.26, IQR 0.24-0.28) when compared with the Controls and the EPLs (p < 0.05). There was no significant difference in any of the inbreeding indices between the EPLs and Controls. The MLPLs had a significantly higher proportion of long (>10 Mb) ROH (2.5%, IQR 1.6-3.6) than the Controls (1.7%, IQR 0.6-2.5), p = 0.001. No unique ROHs were found in the EPL or MLPL populations.

MAIN LIMITATIONS

SNP-array data does not allow analysis of every base in the sequence.

CONCLUSIONS

This first study of the effect of genomic inbreeding levels on pregnancy loss showed that inbreeding is a contributor to MLPL, but not EPL in the UK Thoroughbred population. Mating choices remain critical, because inbreeding may predispose to MLPL by increasing the risk of homozygosity for specific lethal allele(s).

El Hierro Genome Study: A Genomic and Health Study in an Isolated Canary Island Population

El Hierro is the smallest and westernmost island of the Canary Islands, whose population derives from an admixture of different ancestral components and that has been subjected to genetic isolation. We established the "El Hierro Genome Study" to characterize the health status and the genetic composition of ~10% of the current population of the island, accounting for a total of 1054 participants. Detailed demographic and clinical data and a blood sample for DNA extraction were obtained from each participant. Genomic genotyping was performed with the Global Screening Array (Illumina). The genetic composition of El Hierro was analyzed in a subset of 416 unrelated individuals by characterizing the mitochondrial DNA (mtDNA) and Y-chromosome haplogroups and performing principal component analyses (PCAs). In order to explore signatures of isolation, runs of homozygosity (ROHs) were also estimated. Among the participants, high blood pressure, hypercholesterolemia, and diabetes were the most prevalent conditions. The most common mtDNA haplogroups observed were of North African indigenous origin, while the Y-chromosome ones were mainly European. The PCA showed that the El Hierro population clusters near 1000 Genomes' European population but with a shift toward African populations. Moreover, the ROH analysis revealed some individuals with an important portion of their genomes with ROHs exceeding 400 Mb. Overall, these results confirmed that the "El Hierro Genome" cohort offers an opportunity to study the genetic basis of several diseases in an unexplored isolated population.

The Maintenance of Deleterious Variation in Wild Chinese Rhesus Macaques

Understanding how deleterious variation is shaped and maintained in natural populations is important in conservation and evolutionary biology, as decreased fitness caused by these deleterious mutations can potentially lead to an increase in extinction risk. It is known that demographic processes can influence these patterns. For example, population bottlenecks and inbreeding increase the probability of inheriting identical-by-descent haplotypes from a recent common ancestor, creating long tracts of homozygous genotypes called runs of homozygosity (ROH), which have been associated with an accumulation of mildly deleterious homozygotes. Counterintuitively, positive selection can also maintain deleterious variants in a population through genetic hitchhiking. Here, we analyze the whole genomes of 79 wild Chinese rhesus macaques across five subspecies and characterize patterns of deleterious variation with respect to ROH and signals of recent positive selection. We show that the fraction of homozygotes occurring in long ROH is significantly higher for deleterious homozygotes than tolerated ones, whereas this trend is not observed for short and medium ROH. This confirms that inbreeding, by generating these long tracts of homozygosity, is the main driver of the high burden of homozygous deleterious alleles in wild macaque populations. Furthermore, we show evidence that homozygous LOF variants are being purged. Next, we identify seven deleterious variants at high frequency in regions putatively under selection near genes involved with olfaction and other processes. Our results shed light on how evolutionary processes can shape the distribution of deleterious variation in wild nonhuman primates.