Sexual functions, semen characteristics and fertility of bulls carrying the 1/29 chromosome translocation

A genomic biomarker for the rapid identification of the rob(1;29) translocation in beef cattle breeds

Robertsonian translocations, specifically rob(1;29) translocation, have reportedly been the most prevalent chromosomal abnormalities in cattle, affecting various breeds and leading to a decrease in fertility and reproductive value. Currently, the identification of rob(1;29) carriers relies on cytogenetic analysis that has limitations in terms of accessibility, cost, and sample requirements. To address these limitations, a novel genomic biomarker was developed in this study for the rapid and precise identification of rob(1;29) carriers. Using q-PCR, a specific copy number variation associated with translocation was targeted, which effectively distinguished between wild-type, homozygous and heterozygous carriers. Crucially, the biomarker can be applied to DNA extracted from various biological matrices, such as semen, embryos, oocytes, milk, saliva, coat, and muscle, and it is compatible with fresh, refrigerated, or frozen samples. Furthermore, this approach offers significant reductions in cost compared to those associated with traditional cytogenetic analysis and provides results within a short turnaround time. The successful development of this genomic biomarker has considerable potential for widespread adoption in screening programs. It facilitates timely identification and management of rob(1;29) carriers while mitigating economic losses and preserving genetic integrity in bovine populations.

Identification of a common haplotype in carriers of rob(1;29) in 32 Italian cattle breeds

Robertsonian translocation 1;29 (rob(1;29)), a widespread chromosomal anomaly affecting cattle fertility, appears to have originated from a common ancestor. This study utilizes routine SNP data to investigate the chromosomal region associated with rob(1;29) and confirm the presence of a shared haplotype among carriers in diverse Italian breeds. Three datasets were employed: Dataset 1 included 151 subjects from 5 beef cattle breeds genotyped with the GGP Bovine 33 k SNP chip; Dataset 2 encompassed 800 subjects from 32 Italian breeds genotyped with the Illumina 50 k SNP chip, sourced from the BOVITA dataset; Dataset 3 combined Dataset 2 with 21 karyologically tested subjects from breeds with a high carrier frequency, genotyped using the Affymetrix 65 K SNP chip. FST analysis pinpointed a distinctive genomic region on the first six Mb of BTA29, the centromeric region involved in the translocation. Haplotype comparisons within this non-recombining region revealed a common haplotype shared among all carriers, supporting the theory of a common ancestor. Principal component and haplotype analysis allowed clear differentiation of rob(1;29) homozygous and heterozygous carriers. Expanding to Dataset 2 revealed rob(1;29) carriers in unexpected breeds, all sharing the same ancestral haplotype. Notably, previously untested breeds, including Cinisara, exhibited a high carrier prevalence (nearly 50%), confirmed by karyological analysis. This study validates the presence of a shared haplotype among all identified rob(1;29) carriers, reinforcing the common ancestor theory as the origin of this translocation's spread throughout the cattle population. Furthermore, it underscores the potential of SNP data analysis as a rapid, accurate, and cost-effective tool for broad rob(1;29) screening, given the translocation's consistent nature across all analyzed breeds.

Molecular Cytogenetics in Domestic Bovids: A Review

The discovery of the Robertsonian translocation (rob) involving cattle chromosomes 1 and 29 and the demonstration of its deleterious effects on fertility focused the interest of many scientific groups on using chromosome banding techniques to reveal chromosome abnormalities and verify their effects on fertility in domestic animals. At the same time, comparative banding studies among various species of domestic or wild animals were found useful for delineating chromosome evolution among species. The advent of molecular cytogenetics, particularly the use of fluorescence in situ hybridization (FISH), has allowed a deeper investigation of the chromosomes of domestic animals through: (a) the physical mapping of specific DNA sequences on chromosome regions; (b) the use of specific chromosome markers for the identification of the chromosomes or chromosome regions involved in chromosome abnormalities, especially when poor banding patterns are produced; (c) better anchoring of radiation hybrid and genetic maps to specific chromosome regions; (d) better comparisons of related and unrelated species by comparative FISH mapping and/or Zoo-FISH techniques; (e) the study of meiotic segregation, especially by sperm-FISH, in some chromosome abnormalities; (f) better demonstration of conserved or lost DNA sequences in chromosome abnormalities; (g) the use of informatic and genomic reconstructions, in addition to CGH arrays, to predict conserved or lost chromosome regions in related species; and (h) the study of some chromosome abnormalities and genomic stability using PCR applications. This review summarizes the most important applications of molecular cytogenetics in domestic bovids, with an emphasis on FISH mapping applications.

Analysis of the Robertsonian (1;29) fusion in Bovinae reveals a common mechanism: insights into its clinical occurrence and chromosomal evolution

The interest in Robertsonian fusion chromosomes (Rb fusions), sometimes referred to as Robertsonian translocations, derives from their impact on mammalian karyotype evolution, as well from their influence on fertility and disease. The formation of a Rb chromosome necessitates the occurrence of double strand breaks in the pericentromeric regions of two chromosomes in the satellite DNA (satDNA) sequences. Here, we report on the fine-scale molecular analysis of the centromeric satDNA families in the Rb(1;29) translocation of domestic cattle and six antelope species of the subfamily Bovinae. We do so from two perspectives: its occurrence as a chromosomal abnormality in cattle and, secondly, as a fixed evolutionarily rearrangement in spiral-horned antelope (Tragelaphini). By analysing the reorganization of satDNAs in the centromeric regions of translocated chromosomes, we show that Rb fusions are multistep, complex rearrangements which entail the precise elimination and reorganization of specific (peri)centromeric satDNA sequences. Importantly, these structural changes do not influence the centromeric activity of the satellite DNAs that provide segregation stability to the translocated chromosome. Our results suggest a common mechanism for Rb fusions in these bovids and, more widely, for mammals in general.

Chromosome Abnormalities and Fertility in Domestic Bovids: A Review

Simple Summary

In domestic bovids, numerical autosome abnormalities have been rarely reported, as they present abnormal animal phenotypes quickly eliminated by breeders. However, numerical abnormalities involving sex chromosomes and structural (balanced) chromosome anomalies have been more frequently detected because they are most often not phenotypically visible to breeders. For this reason, these chromosome abnormalities, without a cytogenetic control, escape animal selection, with subsequent deleterious effects on fertility, especially in female carriers.

Abstract

After discovering the Robertsonian translocation rob(1;29) in Swedish red cattle and demonstrating its harmful effect on fertility, the cytogenetics applied to domestic animals have been widely expanded in many laboratories in order to find relationships between chromosome abnormalities and their phenotypic effects on animal production. Numerical abnormalities involving autosomes have been rarely reported, as they present abnormal animal phenotypes quickly eliminated by breeders. In contrast, numerical sex chromosome abnormalities and structural chromosome anomalies have been more frequently detected in domestic bovids because they are often not phenotypically visible to breeders. For this reason, these chromosome abnormalities, without a cytogenetic control, escape selection, with subsequent harmful effects on fertility, especially in female carriers. Chromosome abnormalities can also be easily spread through the offspring, especially when using artificial insemination. The advent of chromosome banding and FISH-mapping techniques with specific molecular markers (or chromosome-painting probes) has led to the development of powerful tools for cytogeneticists in their daily work. With these tools, they can identify the chromosomes involved in abnormalities, even when the banding pattern resolution is low (as has been the case in many published papers, especially in the past). Indeed, clinical cytogenetics remains an essential step in the genetic improvement of livestock.

Decoding the Role of Satellite DNA in Genome Architecture and Plasticity-An Evolutionary and Clinical Affair

Repetitive DNA is a major organizational component of eukaryotic genomes, being intrinsically related with their architecture and evolution. Tandemly repeated satellite DNAs (satDNAs) can be found clustered in specific heterochromatin-rich chromosomal regions, building vital structures like functional centromeres and also dispersed within euchromatin. Interestingly, despite their association to critical chromosomal structures, satDNAs are widely variable among species due to their high turnover rates. This dynamic behavior has been associated with genome plasticity and chromosome rearrangements, leading to the reshaping of genomes. Here we present the current knowledge regarding satDNAs in the light of new genomic technologies, and the challenges in the study of these sequences. Furthermore, we discuss how these sequences, together with other repeats, influence genome architecture, impacting its evolution and association with disease.

Fatal Outcome in a Newborn Calf Associated with Partial Trisomy 25q and Partial Monosomy 11q, 60,XX,der(11)t(11;25)(q11;q14∼21)

A newborn calf of the Agerolese cattle breed underwent clinical cytogenetic investigation because of hyperflexion of the forelimbs, red eyes and the inability to stand. Anamnesis revealed that the mother, phenotypically normal, carried a chromosomal aberration. The newborn died after 2 weeks, and no remarkable alterations were found by the veterinarian on postmortem examination. The mother was a carrier of a reciprocal balanced translocation rcp(11;25)(q11,q14∼21) detected after a cytogenetic investigation in 2011; however, the analysis of the newborn revealed a different chromosomal aberration with partial trisomy of chromosome 25 and partial monosomy of chromosome 11. In fact, the results showed both chromosomes 25, one chromosome 11 and only one long derivative chromosome (der11). FISH analysis, performed using BAC clones, confirmed the chromosomes and their regions involved. Finally, both the localization of the breakpoints on band q11 (centromere) of chromosome 11 and band q14-21 of chromosome 25, and the complete loss of the der25 identified the aberration as an unbalanced translocation 60,XX,der(11)t(11;25)(q11;q14∼21). A comparison with human chromosomes was also performed to search for similarities and possible genes involved in order to study their effects, thus extending the knowledge of these aberrations by case reports.

Genomic analysis of cattle rob(1;29)

Robertsonian translocation (rob) involving chromosomes 1 and 29 represents the most frequent chromosome abnormality observed in cattle breeds intended for meat production. The negative effects of this anomaly on fertility are widely demonstrated, and in many countries, screening programs are being carried out to eliminate carriers from reproduction. Although rob(1;29) was first observed in 1964, the genomic structure of this anomaly is partially unclear. In this work, we demonstrate that, during the fusion process, around 5.4 Mb of the pericentromeric region of BTA29 moves to the q arm, close to the centromere, of rob(1;29). We also clearly show that this fragment is inverted. We find that no deletion/duplication involving sequences reported in the BosTau6 genome assembly occurred during the fusion process which originates this translocation.

Reciprocal translocations in cattle: frequency estimation

Chromosomal anomalies, like Robertsonian and reciprocal translocations, represent a big problem in cattle breeding as their presence induces, in the carrier subjects, a well-documented fertility reduction. In cattle, reciprocal translocations (RCPs, a chromosome abnormality caused by an exchange of material between non-homologous chromosomes) are considered rare as to date only 19 reciprocal translocations have been described. In cattle, it is common knowledge that the Robertsonian translocations represent the most common cytogenetic anomalies, and this is probably due to the existence of the endemic 1;29 Robertsonian translocation. However, these considerations are based on data obtained using techniques that are unable to identify all reciprocal translocations, and thus, their frequency is clearly underestimated. The purpose of this work is to provide a first realistic estimate of the impact of RCPs in the cattle population studied, trying to eliminate the factors that have caused an underestimation of their frequency so far. We performed this work using a mathematical as well as a simulation approach and, as biological data, we considered the cytogenetic results obtained in the last 15 years. The results obtained show that only 16% of reciprocal translocations can be detected using simple Giemsa techniques, and consequently, they could be present in no <0.14% of cattle subjects, a frequency five times higher than that shown by de novo Robertsonian translocations. This data is useful to open a debate about the need to introduce a more efficient method to identify RCP in cattle.

Phylogenomic study of spiral-horned antelope by cross-species chromosome painting

Chromosomal homologies have been established between cattle (Bos taurus, 2n = 60) and eight species of spiral-horned antelope, Tribe Tragelaphini: Nyala (Tragelaphus angasii, 2n = 55male/56female), Lesser kudu (T. imberbis, 2n = 38male,female), Bongo (T. eurycerus, 2n = 33male/34female), Bushbuck (T. scriptus, 2n = 33male/34female), Greater kudu (T. strepsiceros, 2n = 31male/32female), Sitatunga (T. spekei, 2n = 30male,female) Derby eland (Taurotragus derbianus 2n = 31male/32female) and Common eland (T. oryx 2n = 31male/32female). Chromosomes involved in centric fusions in these species were identified using a complete set of cattle painting probes generated by laser microdissection. Our data support the monophyly of Tragelaphini and a clade comprising T. scriptus, T. spekei, T. euryceros and the eland species T. oryx and T. derbianus, findings that are largely in agreement with sequence-based molecular phylogenies. In contrast, our study suggests that the arid adaptiveness of T. oryx and T. derbianus is recent. Finally, we have identified the presence of the rob(1;29) fusion as an evolutionary marker in most of the tragelaphid species investigated. This rearrangement is associated with reproductive impairment in cattle and raises questions whether subtle distinctions in breakpoint location or differential rescue during meiosis underpin the different outcomes detected among these lineages.

Chromosomal abnormalities, meiotic behavior and fertility in domestic animals

Since the advent of the surface microspreading technique for synaptonemal complex analysis, increasing interest in describing the synapsis patterns of chromosome abnormalities associated with fertility of domestic animals has been noticed during the past three decades. In spite of the number of scientific reports describing the occurrence of structural chromosome abnormalities, their meiotic behavior and gametic products, little is known in domestic animal species about the functional effects of such chromosome aberrations in the germ cell line of carriers. However, some interesting facts gained from recent and previous studies on the meiotic behavior of chromosome abnormalities of domestic animals permit us to discuss, in the frame of recent knowledge emerging from mouse and human investigations, the possible mechanism implicated in the well known association between meiotic disruption and chromosome pairing failure. New cytogenetic techniques, based on molecular and immunofluorescent analyses, are allowing a better description of meiotic processes, including gamete production. The present communication reviews the knowledge of the meiotic consequences of chromosome abnormalities in domestic animals.

Veterinary cytogenetics: past and perspective

Cytogenetics was conceived in the late 1800s and nurtured through the early 1900s by discoveries pointing to the chromosomal basis of inheritance. The relevance of chromosomes to human health and disease was realized more than half a century later when improvements in techniques facilitated unequivocal chromosome delineation. Veterinary cytogenetics has benefited from the information generated in human cytogenetics which, in turn, owes its theoretical and technical advancement to data gathered from plants, insects and laboratory mammals. The scope of this science has moved from the structure and number of chromosomes to molecular cytogenetics for use in research or for diagnostic and prognostic purposes including comparative genomic hybridization arrays, single nucleotide polymorphism array-based karyotyping and automated systems for counting the results of standard FISH preparations. Even though the counterparts to a variety of human diseases and disorders are seen in domestic animals, clinical applications of veterinary cytogenetics will be less well exploited mainly because of the cost-driven nature of demand on diagnosis and treatment which often out-weigh emotional and sentimental attachments. An area where the potential of veterinary cytogenetics will be fully exploited is reproduction since an inherited aberration that impacts on reproductive efficiency can compromise the success achieved over the years in animal breeding. It is gratifying to note that such aberrations can now be tracked and tackled using sophisticated cytogenetic tools already commercially available for RNA expression analysis, chromatin immunoprecipitation, or comparative genomic hybridization using custom-made microarray platforms that allow the construction of microarrays that match veterinary cytogenetic needs, be it for research or for clinical applications. Judging from the technical refinements already accomplished in veterinary cytogenetics since the 1960s, it is clear that the importance of the achievements to date are bound to be matched or out-weighed by what awaits to be accomplished in the not-too-far future.

Detection of translocation rob(1;29) in bull sperm using a specific DNA probe

The Robertsonian translocation rob(1;29), connected with reduced fertility, is widespread in different cattle breeds all over the world. After laser microdissection, DOP-PCR, cloning and sequencing, a highly sensitive translocation-specific DNA probe, suitable for detection of rob(1;29) in cattle metaphase and interphase cells, including spermatozoa was designed. Sperm samples of five heterozygous translocation carriers were analyzed using this probe and a control probe for chromosome 6. One thousand decondensed spermatozoa from each bull were scored. Signals of the translocation-specific probe were detected in 48.8, 50.9, 50.1, 51.8, and 54.8% of spermatozoa, respectively. In contrast, semen samples from five chromosomally normal bulls showed only signals of the control probe for chromosome 6. Semen from a chimeric (XX/XY) bull, showing 57.5% of 59,XX,rob(1;29) and 42.5% of 60,XY cells in cultured peripheral lymphocytes, was also examined using this probe. No sperm head with signal of the translocation-specific probe was observed among 1,000 spermatozoa analyzed in this bull, demonstrating that female cells do not pass through the process of spermatogenesis.

Frequency and distribution of rob(1;29) in eight Portuguese cattle breeds

Cytogenetic investigations performed in eight Portuguese cattle breeds revealed the presence of rob(1;29) in both heterozygous and homozygous conditions in all, and five breeds, respectively, with variable percentages of carriers as follows: 41.0% in Arouquesa, 69.9% in Barrosa, 39.4% in Maronesa, 2.8% in Mirandesa, 8.5% in Marinhoa, 1.8% in Mertolenga, 21.3% in Raca Brava and 21.5% in Alentejana. CBA- and RBA-banding were performed to ascertain the chromosomes involved in the chromosome abnormality. A total of 1,626 animals were investigated. Reproductive parameters (number of calves per 100 cows) were higher in Mirandesa (80%) when compared with both Maronesa (75%) and Barrosa (70%) breeds, underlining that rob(1;29) reduces fertility in the carriers.

A cattle breed close to 58 diploid number due to high frequency of rob(1;29)

Barrosa cattle, reared in the north of Portugal primarily for meat production, number about 40,000 (about 6% of all cattle in Portugal). Their fertility (number of calves per 100 cows) varies from 60% to 80% and is lower than that of other Portuguese cattle breeds. 195 animals (28 males and 167 females), randomly selected from a large area, were sampled for cytogenetical investigation. The results were the following: (a) 68 (34.9%) animals (7 males and 61 females) had normal karyotypes; (b) 127 (65.1%) were found to be carriers of rob(1; 29), as shown by G- and R-banding; (c) 102 (52.3%) animals (17 (8.7%) males and 85 (43.6%) females) were heterozygous carriers; (d) 25 (12.8%) animals (4 (2%) males and 21 (10.8%) females) were homozygous carriers. C-banding patterns revealed one block of constitutive heterochromatin (HC) in the proximal q-arm region of the translocated chromosome.

New Robertsonian translocation chromosomes in captive Thai gaur (Bos gaurus readei)

Robertsonian translocation have been well documented in domestic cattle, with the most commonly occurring fusion involving chromosomes 1 and 29. The widespread nature of this translocation is indicative of its ancient origin. Fifty Giemsa's stained metaphase spreads derived from lymphocyte cultures of the Thai gaur were analyzed for each animal. The Thai gaur had diploid chromosome number of 2n = 57 in male and 2n = 56 in female instead of the normal 2n = 58. The 2n = 57 in male chromosomes presence of an extra submetacentric chromosome and loss of two acrocentric chromosomes was observed [XY, 57, rob (1;29)]. The 2n = 56 in female chromosomes presence of two extra submetacentric chromosomes and loss of four acrocentric chromosomes was observed [XX, 56, rob (1;29)]. Results from the Giemsa's stained analyses confirm that the two autosomes (2n = 57) and four autosomes (2n = 56) involved in the translocation are the bovine homologues 1 and 29.

A new case of reciprocal translocation in a young bull: rcp(11;21)(q28;q12)

Routine cytogenetic investigations of the Chianina cattle (BTA) breed revealed the presence of longer and smaller chromosomes than the largest (BTA1) and smallest (BTA29) chromosomes in the cells of a young, normal-looking bull used for reproduction. Application of both RBA-banding and Ag-NOR techniques, as well as the use of the FISH technique and specific molecular markers of both BTA11 (IL1B, ASS and LGB) and BTA21 (SERPINA and D21S45) established that these two abnormal chromosomes were the product of a reciprocal translocation between BTA11 and BTA21. Both der(11) and der(21) were C-band positive and the chromosome regions affected were rcp(11;21)(q28;q12). The young bull had a normal body conformation, including external genitalia, normal levels of testosterone (as in the control) and non-detectable levels of both 17 beta-estradiol and progesterone (as in the control). The animal never showed libido in the presence of both males and females in oestrus. After slaughter at 18 months, histological evaluation revealed normal organized testes, seminiferous tubules and epididymis but with poor proliferative germ cells consisting mainly of spermatogonia, middle pachytene spermatocytes and early spermatids with late spermatids and spermatozoa being very rare.

Cloning in companion animal, non-domestic and endangered species: can the technology become a practical reality?

Somatic cell nuclear transfer (SCNT) can provide a unique alternative for the preservation of valuable individuals, breeds and species. However, with the exception of a handful of domestic animal species, successful production of healthy cloned offspring has been challenging. Progress in species that have little commercial or research interest, including many companion animal, non-domestic and endangered species (CANDES), has lagged behind. In this review, we discuss the current and future status of SCNT in CANDES and the problems that must be overcome to improve pre- and post-implantation embryo survival in order for this technology to be considered a viable tool for assisted reproduction in these species.

Cattle rob(1;29) originating from complex chromosome rearrangements as revealed by both banding and FISH-mapping techniques

Sixteen carriers of rob(1;29) (one of which was homozygous) from six different breeds (four Italian and two Portuguese), two heterozygous carriers of rob(26;29), three river buffaloes and two sheep were cytogenetically investigated in this study by using banding and FISH-mapping techniques (the latter only in cattle and river buffalo). Single- and dual- colour FISH were used with bovine probes containing both INRA143 (mapping proximally to BTA29) and bovine satellite (SAT) DNA SAT I, SAT III and SAT IV (mapping at the centromeric regions of cattle chromosomes). The combined use of these probes, the comparison of rob(1;29) with the dicentric rob(26;29) and with both river buffalo and sheep chromosomes (biarmed pairs) allowed us to hypothezise that rob(1;29) originated from complex chromosomal rearrangements through at least three sequential events: (a) centric fusion with the formation of a dicentric chromosome; (b) formation of a monocentric chromosome with loss of SAT I from both BTA1 and BTA29, most of SAT IV from BTA29 and, probably, some repeats of SAT III from BTA1; (c) double pericentric inversion or, more probably, a chromosome transposition of a small chromosome segment containing INRA143 from proximal p-arms to proximal q-arm of the translocated chromosome.

Sperm nuclei analysis of 1/29 Robertsonian translocation carrier bulls using fluorescence in situ hybridization

In 1964, Gustavsson and Rockborn first described the 1/29 Robertsonian translocation in cattle. Since then, several studies have demonstrated the negative effect of this particular chromosomal rearrangement on the fertility of carrier animals. During the last decade, meiotic segregation patterns have been studied on human males carrying balanced translocations using FISH on decondensed sperm nuclei. In this work, we have applied the 'Sperm-FISH' technique to determine the chromosomal content of spermatozoa from two bulls heterozygous for the 1/29 translocation and one normal bull (control). 5425 and 2702 sperm nuclei were scored, respectively, for the two heterozygous bulls, using whole chromosome painting probes of chromosomes 1 and 29. Very similar proportions of normal (or balanced) spermatozoa resulting from alternate segregation were observed (97.42% and 96.78%). For both heterozygous bulls, the proportions of nullisomic and disomic spermatozoa did not follow the theoretical 1:1 ratio. Indeed, proportions of nullisomic spermatozoa were higher than those of disomic sperma tozoa (1.40% vs 0.09% (bull 1) and 1.29% vs 0.15% (bull 2) for BTA1, and 0.65% vs 0.40% (bull 1) and 1.11% vs 0.63% (bull 2) for BTA29). The average frequencies of disomic and diploid spermatozoa in the normal bull were 0.11% and 0.05%, respectively.

Frequency and distribution of rob (1;29) in three Portuguese cattle breeds

Representative samples of Portuguese cattle from Barrosã, Maronesa, and Mirandesa breeds underwent cytogenetic investigation. Banding showed that 134 (65.0%) Barrosas, 74 (40.2%) Maronesas and 4 (1.6%) Mirandesas carried rob (1;29). The frequency of this translocation in the three breeds (39% in Barrosas, 23% in Maronesas, and 1% in Mirandesas) was in a genetic Hardy-Weinberg equilibrium for the three karyological forms (2n = 60, 2n = 59 and 2n = 58), strongly supporting the hypothesis for an ancient origin of this translocation and the hypothesis of the origin of Maronesas from Barrosã and Mirandesa cross-breeding.

A new centric fusion translocation in cattle, rob(16;18)

A Barrosã bull (Portugal) has been found to carry a new Robertsonian translocation involving chromosomes 16 and 18 of standard cattle karyotype, as demonstrated by GBG- and RBG-banding techniques. C-banding patterns revealed the dicentric nature of this translocation. A comparison between normal cattle chromosome 16 and the q-arms of translocation chromosome and river buffalo chromosome 5 revealed the same G- and R-banding patterns, with only exception of a pericentromeric G-positive band which has been lost in river buffalo 5q and conserved in normal cattle chromosome 16 and rob(16;18) q-arms.

A new Robertsonian translocation in cattle, rob(16;20)

A new centric fusion translocation, rob(16;20), was discovered in a phenotypically normal bull. C-banding revealed the dicentric nature of this centric fusion. This bull is a descendant of a German red pied bull and a Czechoslovakian red pied cow. Its mother and 26 half-brothers had normal karyotypes, indicating that this translocation arose "de novo".

Incidence of 1/29 translocation in Bolivian Creole and Brahman Yacumeño cattle

In Bolivia, four different Creole cattle breeds can be found, as well as other European and Zebu breeds adapted to local environments. The relationship between the occurrence of the 1/29 translocation and subfertility is well known, and analysis of Y chromosome morphology is useful to determine a possible introgression with Bos indicus. The incidence of the 1/29 translocation was analyzed in four Bolivian Creole cattle breeds and the Brahman Yacumeño population, as well as on four farms with phenotypical Creole-type cattle. In 259 (164 dams and 95 sires) Bolivian Creole cattle, 10.42% of the individuals demonstrated the 1/29 translocation, with a variation from 0 to 28.20% between the breeds. In contrast, 43 (19 dams and 24 sires) Yacumeño Brahman and the Creole-type cattle did not show the centric fusion. The highly significant differences between Creole cattle breeds in relation to the incidence of 1/29 translocation could be a consequence of factors such as founder group, genetic drift, and selection. The low frequency observed in the Saavedreñio Creole dairy cattle might be explained by its breeding under a more intensive system, and selection according to milk yield and fertility traits. Finally, no relation between acrocentric Y chromosomes and 1/29 translocation was observed.

X-autosome translocation and low fertility in a family of crossbred cattle

An investigation was carried out on a family of Limousin-Jersey crossbreds exhibiting low fertility in the females, to determine the impact of a previously identified X-autosome translocation (X-AT) on the reproductive performance of the carrier cows. Three of the identified translocation carriers, including a cow and two of her daughters, were maintained at our University Research Station and artificially inseminated periodically with semen from different bulls of known fertility. Attempts to breed the X-AT carriers resulted in high rates of return to estrus between days 28 and 60, abortions between days 121 and 235 after insemination, and a total of 13 live births including 4 translocation carrier calves. Results of superovulation and embryo retrieval trials on X-AT carriers revealed significantly higher proportions of unfertilized and uncleaved ova and abnormal embryos compared to those from normal cows, and no pregnancy in the recipients transferred with morphologically normal blastocysts from X-AT carriers. While the higher rates of failed fertilization and cleavage, abnormal embryos and return to estrus in X-AT carriers could be attributed to chromosome imbalance expected in their gametes, the relatively high prevalence of abortion (late in gestation) was unexpected. Our observations on the fetuses expelled by X-AT carriers after 5 months of gestation indicated that a majority (three out of four) of these fetuses were products of abnormal (3:1) segregation in meiosis I and that these chromosomally unbalanced (hyperdiploid) conceptuses were able to survive early embryogenesis and fetal life up to the end of the second trimester. We hypothesize that their relatively long in utero life and the absence of any overt birth defects may be attributable to the type of chromosomes over-represented in these fetuses and that their eventual expulsion may have been the result of selection against the clonal population of cells in which the altered X carrying a segment of chromosome 23 (Xp(+)), remained inactive.

Cytogenetic survey of Holstein bulls at a commercial artificial insemination company to determine prevalence of bulls with centric fusion and chimeric anomalies

OBJECTIVE

To determine prevalence of Holstein bulls with chromosomal anomalies, particularly the 1/21 centric fusion (CF), at a commercial artificial insemination (AI) company in the United States.

DESIGN

Cross-sectional cytogenetic prevalence study.

ANIMALS

All 606 Holstein bulls at a commercial AI company were cytogenetically screened to detect CF, chimerism, and other chromosomal abnormalities.

PROCEDURE

Lymphocytes from heparinized blood samples were cultured by standard cytogenetic techniques, and chromosome spreads were prepared for microscopic examination. Chromosomal abnormalities were detected by examining 10 chromosome spreads per bull. Pedigree analysis was performed.

RESULTS

None of the bulls had any type of CF. However, 6 bulls were identified as chimeras (i.e., contained lymphocytes with male [XY] and female [XX] chromosomes). One bull was sire or maternal grandsire to 85 of the bulls tested, and 739 of 1,212 (61%) sire and maternal-grandsire possibilities were accounted for by just 18 bulls.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of these results supports previous indications that CF is extremely rare in Holstein bloodlines available commercially via AI in the United States. However, chimeric bulls are more common, and they reportedly have decreased reproductive performance. Therefore, identification of chimeric sires in the AI facility reported here and the possibility of de novo onset of CF at any time indicates that early cytogenetic screening should be encouraged for prospective bulls intended for use in AI programs.

A potential relationship between the 16;20 and 14;20 Robertsonian translocations and low in vitro embryo development

A possible effect of 16;20 and 14;20 Robertsonian translocations on the development of bovine oocytes matured and fertilized in vitro was assessed on the basis of embryo yield and blastocyst formation. Oocytes fertilized with semen from 2 bulls (A and B), which were heterozygous for these translocations, showed a significantly lower cleavage rate (36.3 +/- 2.25%; 39.8 +/- 3.88%) and percentage of blastocysts (3.7 +/- 1.24%; 3.2 +/- 1.20%) than those fertilized with semen from a bull (C) with a normal karyotype (control, 58.1 +/- 2.14%; 20.1 +/- 1.92%; P < 0.01). There was also a difference in the rate of further blastocyst development between the tested bulls and the control. The rates of expanded blastocysts were 6.6 and 11.1% for Bulls A and B, respectively, and 38.7% for the control bull on Day 7; while on Day 8 these values were 41.7 and 55.5% vs 76.0%. These results demonstrated that in the bulls carrying the 16;20 and 14;20 translocations, in vitro preimplantation embryo development was reduced, probably due to genetically unbalanced spermatozoa.

A new centric fusion translocation in cattle: rob (13;19)

A new Robertsonian translocation has been found in cattle. A bull from Marchigiana breed (central Italy) was found to be a heterozygous carrier of a centric fusion translocation involving cattle chromosomes 13 and 19 according to RBA-banding and cattle standard nomenclatures. CBC-banding revealed the dicentric nature of this new translocation, underlining the recent origin of this fusion. In fact, both the bull's parents and relatives had normal karyotypes. In vitro fertilization tests were also performed in the bull carrying the new translocation, in two bulls with normal karyotypes (control) and in four other bulls carrying four different translocations.

Fertility effects of the 14;20 Robertsonian translocation in cattle

Superovulation and embryo collection procedures were used to study the effect of the 14;20 Robertsonian translocation on fertility and embryo viability. Karyotypes were successfully completed on cells from 77 of the 279 embryos prepared for such analysis. Embryos from 4 cows heterozygous for the translocation were studied. Two bulls with the same condition were studied by using their semen in artificial insemination of cows with normal karyotypes. The proportions of fertilized ova and transferable embryos were not different between cows with the 14;20 translocation and those with normal karyotypes, indicating that fertilization rates were not affected by the translocation. Twenty-two percent of the embryos which were karyotyped had an unbalanced karyotype and would theoretically not have survived to term. All of the theoretically predicted chromosome complements from such a translocation were observed as were three 58,XX,t karyotypes and a 58,XX karyotype. There was no difference in the percentage of embryos with abnormal karyotypes whether the cow or bull was the carrier. Results therefore indicate that fertility is rather severely impaired in carriers of the 14;20 translocation, as was observed with the 1;29 translocation, with most loss due to embryo mortality rather than a lowered conception rate.

Y-Chromosome morphology and incidence of the 129 translocation in argentine creole bulls

The Argentine Creole is a local breed of cattle with high reproductive performance. This breed also shows resistance to many subtropical diseases. The cytogenetic status of the Argentine Creole, in particular the incidence of 1/29 translocation and Y-chromosome morphology, is not known in Argentina. Taking these factors into account, the cytogenetic study of 36 Argentinian Creole bulls was carried out. Heparinized blood samples were obtained and cultured for chromosome analysis. The results showed the absence of the 1/29 translocation in all the bulls analyzed and the presence of a submetacentric Y chromosome.

Effects of the Robertsonian translocation on fertilization rates and preimplantation development of bovine oocytes in vitro

A study was conducted to investigate the effect of the 7/21 Robertsonian translocation on fertilization and subsequent development of bovine oocytes matured in vitro. Semen from Japanese Black bulls, 2 with a normal karyotype (Bulls A and B) and 2 that were heterozygous for the 7/21 translocation (Bulls C and D), was used in this study. In vitro matured bovine oocytes were inseminated with frozen-thawed sperm capacitated with heparin. After insemination, oocytes were cultured at 38.5 degrees C on a monolayer of cumulus cells in TCM-199 supplemented with 5% superovulated cow serum and 0.5 mM sodium pyruvate in an atmosphere of 2% CO2 in air. Cleavage rate was evaluated at 54 h after insemination, and development of embryos to the blastocyst stage was observed 7 to 10 d post insemination. There was no difference in the fertilization rate among the 4 bulls. Although the cleavage rate of oocytes inseminated with semen from Bull C (heterozygote) was lower (P < 0.05) than that obtained with semen from Bull B (normal), the blastocyst formation rate did not differ among the 4 bulls. These results indicate that the 7/21 Robertsonian translocation had no effect on the fertilization and blastocyst formation rates of bovine in vitro-matured oocytes.

Additional evidence of the formation of unbalanced embryos in cattle with the Robertsonian translocation

To confirm the effect of the 7 21 Robertsonian translocation on fertility in Japanese Black Cattle, cytogenetic studies were performed on embryos collected from the following 3 mating groups: normal bull cross normal cow, translocation carrier bull cross normal cow, and normal bull cross translocation carrier cow. All the analyzable embryos showed normal chromosome complements when the parents had a normal karyotype. In the group sired by the 7 21 translocation heterozygous bulls, a total of 56 embryos had metaphases suitable for chromosome analyses. Out of these embryos, 28 had normal chromosome complements and 25 were embryos with a balanced karyotype. However, 3 (5.4%) were monosomic and trisomic embryos, presumably resulting from the fertilization of normal ova by aneuploid spermatozoa. Unbalanced embryos were also observed in the chromosome analyses of embryos derived from the 7 21 translocation heterozygous cows. These results suggest that the 7 21 translocation in the heterozygous state may be associated with a slight reduction in reproductive efficiency.

Incidence of translocation in Venezuelan Creole bulls

The Venezuelan Creole breed cattle is a Bos taurus well adapted to tropical conditions; however, it has demonstrated a low fertility rate. Recently, improvement in animal production by selection based on chromosomal analysis has allowed for the erradication of abnormalities involved in fertility problems, especially that of the 1 29 translocation. In the present work chromosomal analyses were carried out on 60 Creole bulls. Heparinized peripheral blood cells were cultured rendering metaphase spreads and subsequently stained by G- and C-banding techniques. The 1 29 translocation was observed in 13 of the 60 bulls. The occurrence of this translocation in Creole cattle is discussed.

Meiosis in chromosomally heteromorphic goitered gazelle, Gazella subgutturosa (Artiodactyla, Bovidae)

Chromosomal-pairing behaviour was studied in the spermatocytes of individual goitered gazelles which were heteromorphic for a 14/15 Robertsonian translocation and which possessed an autosome-to-X translocation. Both translocations exhibited trivalent pairing configurations in pachytene and diakinesis/metaphase I nuclei. Synapsis of the sex chromosomes during pachynema was followed by end-to-end association of the X and Y during diakinesis/metaphase I. The only univalents identified were of the Y chromosome; Y univalency ranged from 15.9% at pachynema to 5.7% at diakinesis/metaphase I. Robertsonian trivalents exhibited evidence of synaptic adjustment in the paracentromeric region. Chiasmata were formed in most bivalents and trivalents; chiasmata were restricted to the autosomal portion of the autosome-to-XY trivalent. Analysis of metaphase II configurations (secondary spermatocytes) revealed no nondisjunction in individuals homozygous or heterozygous for the Robertsonian translocation. These data are consistent with the hypothesis that neither the autosomal nor the gonosomal heteromorphism reduces the meiotic fitness of male goitered gazelles.

Use of semen from a bull heterozygous for the translocation in an IVF program

In cattle, a translocation of the Robertsonian type between the largest and smallest chromosome leads to a reduction in fertility. This is substantiated by reduced nonreturn rates in daughter groups of bulls carrying the 1 29 translocation and in the heterozygous bulls themselves. This reduction in fertility is thought to be due to the early death of embryos with unbalanced karyotypes. The influence of semen from a bull known to be heterozygous for the 1 29 translocation on the outcome of a bovine IVF program was investigated. There was a significant difference (P<0.005) in terms of cleavage rate (59.8 vs 71.1%) and blastocyst rate (12.0 vs 20.0%) between the carrier and control bull, respectively. There was no difference in blastocyst quality as measured by cell number. The results observed in vitro are consistent with the field fertility records of the 2 bulls in terms of nonreturn rates (59.2 vs 70.6%, for the carrier and control bull, respectively).

Does the Robertsonian translocation affect the fertility of Blonde d'Aquitaine breed bulls?

The effects of the 1/29 translocation upon male fertility were studied by analysis of the results of 1,350,385 first artificial inseminations with the semen of Blonde d'Aquitaine or Coopelso-93 bulls (n=220). A binomial logit model was designed, taking into account the translocation of sire, breed of sire, breed of dam, year, AI center, and all interactions between translocation, and breed of sire, and breed of dam. Male fertility was not affected by the 1/29 translocation, and the nonreturn rates at 60 to 90 days of Blonde d'Aquitaine females inseminated with the semen of carrier bulls (135,632 first AI) or noncarrier bulls (585,949 first AI) were 74.88% and 74.75%, respectively.

Embryonic loss in superovulated cattle caused by the 1;29 Robertsonian translocation

The effect of the 1;29 Robertsonian translocation on fertility was studied using embryos resulting from matings of nine carrier cows and two carrier bulls. Embryos were collected from the following three mating groups utilizing superovulation: normal bull cross normal cow, normal bull cross translocation carrier cow, and translocation carrier bull cross normal cow. The proportion of ova which were fertilized did not vary among the groups, indicating that fertilization rates were not affected by the translocation. The translocation cows did yield fewer embryos on average than did cows with normal karyotypes, which may suggest ovulation rates are reduced (at least after superovulation attempts) in cattle carrying the 1;29 translocation. Twenty of 39 embryos successfully karyotyped had abnormal chromosome complements. All four of the theoretically predicted karyotypes and two additional abnormal combinations were found. Eight of 39 (20.5%) embryos karyotyped had unbalanced karyotypes which would have resulted in embryonic loss. The proportion of embryos with unbalanced karyotypes, was slightly higher when the cow (36%) carried the translocation than when the bull (19%) did. Results of this study indicate that fertility is impaired due to the presence of this translocation. The major loss in reproductive potential appears to be due to embryonic loss rather than fertilization failure.

Genetic diseases of sheep and goats

Congenital malformations and inherited disorders constitute a substantial proportion of the afflictions seen in sheep and goats. Of these, malformations tend to be similar in both species, whereas the genetic diseases encountered to date, with the exception of a few, are different. Of the 28 genetic diseases of sheep and goats described in this review, 60% and 62.5%, respectively, are monogenic disorders. For a majority of the monogenic recessive disorders encountered in these species, the carrier state is not detectable at present, whereas in others, in which a biochemical lesion is known (dermatosparaxis, erythrocyte glutathione deficiency, globoid cell leukodystrophy and glycogen storage disease), the carrier state is detectable with the aid of enzyme and surface protein markers. The latter group and the dominant disorders (anury, cataract, glomerulonephritis, and lethal grey in sheep; gynecomastia and anotia-microtia complex in goats) are easy to eliminate through selective breeding. The polygenic disorders (entropion, epidermolysis bullosa, hereditary chondrodysplasia, and muscular dystrophy of sheep, and udder problems in goats) are more difficult to eradicate, because the mutant genes responsible for these traits generally do not declare themselves until inbreeding brings together a critical concentration to create a health crisis in some, whereas others, which are only short of a few of these mutant genes, might go totally unaffected and therefore undetected. Chromosome defects of the structural nature (translocations) seen in sheep and goats generally create meiotic disturbances, which in a majority of cases lead to subfertility, whereas sex chromosome aneuploids are generally sterile.(ABSTRACT TRUNCATED AT 250 WORDS)