Twenty Years Later: A Comprehensive Review of the X Chromosome Use in Forensic Genetics

Forensic efficiency and genetic polymorphisms of 12 X-chromosomal STR loci in Northeastern Thai populations

Northeastern Thailand comprises one-third of the country and is home to various populations, with Lao Isan constituting the majority, while others are considered minority groups. Previous studies on forensic short tandem repeats (STRs) in Thailand predominantly focused on autosomal STRs but there was a paucity of X-STRs, exclusively reported from the North and Central regions of the country. In this study, we have newly established a 12 X-STRs from a total of 896 samples from Northeastern Thailand, encompassing Lao Isan as the major group in the region, alongside nine minor populations (Khmer, Mon, Nyahkur, Bru, Kuy, Phutai, Kalueang, Nyaw, and Saek). Across all ten populations, the combined powers of discrimination in both genders were high and the combined mean exclusion chance (MEC) indices calculated for deficiency, normal trio and duo cases were also high (> 0.99999). DXS10148 emerged as the most informative marker, while DXS7423 was identified as the least informative. Genetic comparison based on X-STRs frequency supported genetic distinction of cerain minor groups such as Kuy, Saek and Nyahkur from other northeastern Thai groups as well as genetic differences according to the geographic region of Thai groups (Northeast, North and Central). In sum, the overall results on population genetics are in agreement with earlier reports on other genetic systems, indicating the informativeness of X-STRs for use in anthropological genetics studies. From a forensic perspective, despite the limitations of small sample sizes for minority groups, the present results contribute to filling the gap in the reference X-STRs database of the major group Lao Isan, providing valuable frequency data for forensic applications in Thailand and neighboring countries.

Forensic autosomal and gonosomal short tandem repeat marker reference database for populations in Burkina Faso

Tandem repeat genetic profiles used in forensic applications varies between populations. Despite the diversity and security issues in the Sahel that require the identification of victims (soldiers and civilians), Burkina Faso (BF) remains understudied. To fill this information gap, 396 unrelated individuals from BF were genotyped using a MICROREADER 21 ID System kit. All 20 short tandem repeat (STR) loci tested passed the Hardy-Weinberg equilibrium (HWE) test. The combined powers of exclusion for duos (CPE duos) and trios (CPE trios) for the 20 tested loci were 0.9999998 and 0.9999307, respectively. The probability that two individuals would share the same DNA profiles among the BF population was 9.80898 × 10-26. For the X-chromosome STR analysis, 292 individuals were included in this study using a MICROREADER 19X Direct ID System kit. Among the 19 loci, no significant deviations from HWE test were observed in female samples after Bonferroni correction (p < 0.05/19 = 0.0026), except for loci GATA165B12 and DXS7423. The results showed that the combined power of exclusion (CPE) and the combined power of discrimination in females (CPDF) and males (CPDM) were 0.999999760893, 0.999999999992, and 1, respectively. Comparison with other African sub-populations showed that geographical proximity is a reliable indicator of genetic relatedness.

Genetic analysis of the X chromosome in people with Lewy body dementia nominates new risk loci

Sex influences the prevalence and symptoms of Lewy body dementia (LBD). However, genome-wide association studies typically focus on autosomal variants and exclude sex-specific risk factors. We addressed this gap by performing an X chromosome-wide association study using whole-genome sequence data from 2591 LBD cases and 4391 controls. We identified a significant risk locus within intron 1 of MAP3K15 (rs141773145, odds ratio = 2.42, 95% confidence interval = 1.65-3.56, p-value = 7.0 × 10-6) in female LBD cases conditioned for APOE ε4 dosage. The locus includes an enhancer region that regulates MAP3K15 expression in ganglionic eminence cells derived from primary cultured neurospheres. Rare variant burden testing showed differential enrichment of missense mutations in TEX13A in female LBD cases, that did not reach significance (p-value = 1.34 × 10-4). These findings support the sex-specific effects of genetic factors and a potential role of Alzheimer's-related risk for females with LBD.

Analysis of 12 X-STRs loci in a population from southeastern Brazil

Short tandem repeat (STR) markers on the X chromosome have a high potential for solving complex kinship analysis and individual identification cases. To achieve such purposes, allele and haplotype frequencies for the specific population are necessary. Nonetheless, such frequencies are not always available. Therefore, we obtained haplotypes from 520 unrelated males from four different geographic regions of Espírito Santo - Brazil, using the Investigator Argus X-12 kit. Forensic parameters for linked groups of four X-STR loci are reported. Genetic distance analyzes suggest that ES population is genetically closer to the Italian population and farther from the Mexican one, among the populations analyzed in this study.

An X-STRs analysis of the Iraqi Sorani Kurds

A database for the Iraqi Sorani Kurds, specifically focused on the 12 X-short tandem repeat (STR) loci, has been developed to fascilitate forensic and population genetics investigations. The present study involved genotyping 117 unrelated individuals from the Sorani Kurds ethnic group using the Investigator Argus X-12 QS kit. The analysis revealed that the DXS10135 locus exhibited the highest degree of polymorphism, as indicated by a polymorphism information content (PIC) value of 0.94565 and a gene diversity (GD) value of 0.95623. Conversely, the DXS8378 locus displayed the lowest level of polymorphism, with a PIC value of 0.61026 and a GD value of 0.68170. Notably, two individuals were found to possess a rare allele (allele = 6) at the DXS8378 locus, which was not included in the allelic ladder of the kit. Furthermore, a significant linkage disequilibrium (LD) (p < 0.05/117) was observed between the DXS10103 and DXS10101 loci on linkage group 3 (LG3). The ancestral composition of the five primary geographic regions, namely Africa, Middle East, East Asia, Europe, and South America, was determined through the utilization of the [Formula: see text] ratio. The findings of this analysis revealed that the Middle Eastern populations exhibited the lowest [Formula: see text] ratio, measuring at 0.23243, indicating a relatively lower ancestral diversity. Conversely, the European populations showcased the highest [Formula: see text] ratio, measuring at 0.27122, indicative of a greater ancestral diversity within this region. Additionally, the allelic richness indicators, namely distinctive and private alleles, indicated that Africa and the Middle East displayed the highest levels, while Far East Asia exhibited the lowest. This analysis supports the hypothesis of repeated founder effects during outward migrations, as evidenced by both the ancestry variability and the allelic richness. Consequently, the findings of this study have important implications for forensic genetics and population genetics research, particularly in relation to the consideration of genetic predispositions within specific ethnic groups.

Internal validation of reduced PCR reaction volume of the Qiagen Investigator® Argus X-12 QS Kit from blood samples on FTA cards

The onus of proof in criminal cases is beyond any reasonable doubt, and the issue on the lack of complete internal validation data can be manipulated when it comes to justifying the validity and reliability of the X-chromosomal short tandem repeats analysis for court representation. Therefore, this research evaluated the efficiency of the optimized 60% reduced volumes for polymerase chain reaction (PCR) amplification using the Qiagen Investigator® Argus X-12 QS Kit, as well as the capillary electrophoresis (CE) sample preparation for blood samples on Flinder's Technology Associates (FTA) cards. Good-quality DNA profile (3000-12,000 RFU) from the purified blood sample on FTA card (1.2 mm) were obtained using the optimized PCR (10.0 μL of PCR reaction volume and 21 cycles) and CE (9.0 μL Hi-Di™ Formamide and 0.3 μL DNA Size Standard 550 [BTO] and 27 s injection time) conditions. The analytical and stochastic thresholds were 100 and 200 RFU, respectively. Hence, the internal validation data supported the use of the optimized 60% reduced PCR amplification reaction volume of the Qiagen Investigator® Argus X-12 QS Kit as well as the CE sample preparation for producing reliable DNA profiles that comply with the quality assurance standards for forensic DNA testing laboratories, while optimizing the analytical cost.

Identification of the Remains of an Adult Using DNA from Their Deciduous Teeth as a Reference Sample

In many forensic cases, the identification of human remains is performed by comparing their genetic profile with profiles from reference samples of relatives, usually the parents. Here, we report, for the first time, the identification of the remains of an adult using DNA from the person's deciduous teeth as a reference sample. Fragments of a skeletonized and burned body were found, and a short tandem repeat (STR) profile was obtained. A woman looking for her missing son went to the authorities. When the DNA profile of the woman was compared to a database, a positive match suggested a first-degree kinship with the person to whom the remains belonged. The woman had kept three deciduous molars from her son for more than thirty years. DNA typing of dental pulp was performed. The genetic profiles obtained from the molars and those from the remains coincided in all alleles. The random match probability was 1 in 2.70 × 1021. Thus, the remains were fully identified. In the routine identification of human remains, ambiguous STR results may occur due to the presence of null alleles or other mutational events. In addition, erroneous results can be produced by false matches with close family members or even with people who are completely unrelated to the victim, such that, in some cases, a probability of paternity greater than 99.99% does not necessarily indicate biological paternity. Whenever possible, it is preferable to use reference samples from the putative victim as a source of DNA for identification.

Recombulator-X: A fast and user-friendly tool for estimating X chromosome recombination rates in forensic genetics

Genetic markers (especially short tandem repeats or STRs) located on the X chromosome are a valuable resource to solve complex kinship cases in forensic genetics in addition or alternatively to autosomal STRs. Groups of tightly linked markers are combined into haplotypes, thus increasing the discriminating power of tests. However, this approach requires precise knowledge of the recombination rates between adjacent markers. The International Society of Forensic Genetics recommends that recombination rate estimation on the X chromosome is performed from pedigree genetic data while taking into account the confounding effect of mutations. However, implementations that satisfy these requirements have several drawbacks: they were never publicly released, they are very slow and/or need cluster-level hardware and strong computational expertise to use. In order to address these key concerns we developed Recombulator-X, a new open-source Python tool. The most challenging issue, namely the running time, was addressed with dynamic programming techniques to greatly reduce the computational complexity of the algorithm. Compared to the previous methods, Recombulator-X reduces the estimation times from weeks or months to less than one hour for typical datasets. Moreover, the estimation process, including preprocessing, has been streamlined and packaged into a simple command-line tool that can be run on a normal PC. Where previous approaches were limited to small panels of STR markers (up to 15), our tool can handle greater numbers (up to 100) of mixed STR and non-STR markers. In conclusion, Recombulator-X makes the estimation process much simpler, faster and accessible to researchers without a computational background, hopefully spurring increased adoption of best practices.

The development of the novel 22 X- indel multiplex system for forensic genetics

InDel (Insertions/deletion) markers have been used as an alternative, or as a complementary marker system, to STR markers in human identification due to their advantages such as low mutation rates, no stutter, and potential small amplicon sizes. In forensic sciences, sex chromosomes are widely used in forensic genetics for specific cases. For example, the relationship between father and daughter can be determined by using X-InDels. In this study, we developed a novel 22 X-InDel multiplex system that was identified by two separate assays with fluorescence amplification and capillary electrophoresis detection technology. We chose 22 X-InDel markers based on the following criteria: mean heterozygosity over 30% in Europeans; minimum of 250 Kb differences between each InDel loci; and an amplicon length that was less than 300 bp. We performed an optimization and validation study of 22 X-InDel systems under the following parameters: analytical threshold, sensitivity, precision and accuracy, stochastic threshold, repeatability, and reproducibility. We evaluated the allele frequency of this multiplex system in the Turkish population, and then the population comparisons were carried out on data from 1000 Genome populations (Europe, Africa, America, South Asia, and East Asia). The sensitivity test showed a complete genotyping profile with DNA concentrations as low as 0.5 ng. The heterozygosity ratio of 22 X-InDel loci was determined as 0.4690 and the discrimination power was defined as 0.99. The results show that the new 22 X-InDel multiplex system provides high polymorphism information, and it is a reproducible, accurate, sensitive, and robust system that could be used as an additional tool for kinship testing.

Population genetic analysis of 12 X-STR markers in Slovakia

Background: During the last 20 years, X-chromosomal STR markers have become widely used in forensic genetics and paternity testing. Nevertheless, to exploit their full potential in any given population, a reliable reference dataset needs to be established. Since no relevant studies concerning these markers have been performed on the Slovak population so far, we decided to analyse several commonly used markers in this population.Aim: To create an informative set of Slovak population data concerning X-STR markers.Subjects and methods: We genotyped 378 individuals and analysed 12 loci (DXS10148, DX10135, DXS8378, DXS7132, DXS10079, DXS10074, DXS10103, HPRTB, DXS10101, DXS10146, DXS10134 and DXS742) localised in four distinct linkage groups.Results: Our analysis showed that the most informative marker is DXS10135 (PIC = 0,927) and the most informative linkage group (LG) is LG1 with 149 different haplotypes. This analysis also confirmed linkage disequilibrium for two pairs of markers (DX10101-DX10103 and DX10101-HPRTB) within LG3 in female samples. No statistically significant departure from HWE was observed for any locus. Moreover, the interpopulation comparison of 8 European populations based on haplotype frequencies showed no statistically significant FST values in any LG, except for LG2 in comparison with the German population.Conclusion: We created a haplotype database for forensic analyses and kinship testing in Slovakia, as well as the CE dataset which can be used to further increase the decision power in similar analyses in the future.

Genetic features and phylogenetic relationship analyses of Guizhou Han population residing in Southwest China via 38 X-InDels

Background

The insertion/deletion polymorphism (InDel), an ideal forensic genetic marker with a low spontaneous mutation rate and small amplification product fragments, is widely distributed in the genome, combining the advantages of STR and SNP genetic markers. The X-chromosome has high application value in complex paternity testing, and it is an excellent system for evaluating population admixture and studying evolutionary anthropology. However, further research is needed on the population genetics of X-chromosome InDels (X-InDels).

Methods

In this article, a system composed of 38 X-InDel loci was utilized to analyse and evaluate the forensic parameters of the Guizhou Han population in order to explore its forensic application efficiency.

Results

The results showed that expected heterozygosities spanned from 0.0189 to 0.5715, and the cumulative power of discrimination of the 32 X-InDels and three linkage blocks was 0.9999999954 and 0.999999999999741 for males and females, respectively. The combined mean exclusion chance of these loci for trios and duos is 0.999999 and 0.999747, respectively. Multiple methods like principal component analysis, Fst genetic distance, and phylogenetic reconstruction were employed for dissecting the genetic structure of the Guizhou Han population by comparing it with previously reported populations. As expected, the studied Han population displayed relatively close genetic affinities with the East Asian populations. At the same time, there were obvious genetic differentiations between the Guizhou Han population and other continental populations that were discerned, especially for the African populations.

Conclusions

This study further verified the applicability of 38 X-InDels for human personal identification and kinship analyses of Han Chinese, and also showed the application potential of X-InDels in population genetics.

Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019-2022

This review paper covers the forensic-relevant literature in biological sciences from 2019 to 2022 as a part of the 20th INTERPOL International Forensic Science Managers Symposium. Topics reviewed include rapid DNA testing, using law enforcement DNA databases plus investigative genetic genealogy DNA databases along with privacy/ethical issues, forensic biology and body fluid identification, DNA extraction and typing methods, mixture interpretation involving probabilistic genotyping software (PGS), DNA transfer and activity-level evaluations, next-generation sequencing (NGS), DNA phenotyping, lineage markers (Y-chromosome, mitochondrial DNA, X-chromosome), new markers and approaches (microhaplotypes, proteomics, and microbial DNA), kinship analysis and human identification with disaster victim identification (DVI), and non-human DNA testing including wildlife forensics. Available books and review articles are summarized as well as 70 guidance documents to assist in quality control that were published in the past three years by various groups within the United States and around the world.

Development and forensic efficiency evaluations of a novel multiplex amplification panel of 17 Multi-InDel loci on the X chromosome

Multi-InDel, as the novel genetic markers, showed great potential in forensic research. Whereas, most scholars mainly focused on autosomal Multi-InDels, which might provide limited genetic information in some complex kinship cases. In this study, we selected 17 Multi-InDels on the X chromosome and developed a multiplex amplification panel based on the next-generation sequencing (NGS) technology. Genetic distributions of these 17 loci in Beijing Han, Chinese Southern Han, and the studied Guizhou Han populations revealed that most loci showed relatively high forensic application values in these Han populations. In addition, more allelic variations of some loci were observed in the Guizhou Han than those in Beijing Han and Southern Han populations. Pairwise FST values, multi-dimensional analysis, and phylogenetic tree of different continental populations showed that selected 17 loci generally could differentiate African, European, East Asian, and South Asian populations. To sum up, the developed panel in this study is not only viewed as the high-efficient supplementary tool for forensic individual identification and paternity analysis, but it is also beneficial for inferring biogeographical origins of different continental populations.

Forensic Applications of Markers Present on the X Chromosome

Microsatellite genetic markers are the gold standard for human genetic identification. Forensic analyses around the world are carried out through protocols using the analysis of STR markers in autosomal chromosomes and in the Y chromosome to solve crimes. However, these analyses do not allow for the resolution of all cases, such as rape situations with suspicion of incest, paternity without a maternal sample for comparison, and biological traces with DNA mixture where the profile sought is female, among other situations. In these complex cases, the study of X-chromosome STR markers significantly increases the probability of identification by complementing the data obtained for autosomal and Y-chromosome markers, due to the unique structure of the X chromosome and its exclusive method of inheritance. However, there are currently no validated Brazilian protocols for this purpose, nor are there any population data necessary for statistical analyses that must be included in the issuance of expert reports. Thus, the aim of this article is to provide a literary review of the applications of X-chromosomal markers in population genetics.

Resolving the recombination pattern of 38 X-STRs from Chinese Han three-generation pedigrees

X-chromosomal markers have been proved as a useful tool for solving complex kinship cases due to its sex-linked inheriting feature. Among these markers, tightly linked X-STR clusters forming haplotypes are highly informative. The analysis of the haplotypes requires determination of linkage disequilibrium. In this study, genetic linkage, recombination fractions and mutation rates of 38 X-STR loci in 177 three-generation pedigrees were investigated. Genetic linkage analysis and calculation of recombination fractions were performed within each pair of markers and clusters. Then mutation rates were calculated. The results showed that, a) 22 recombination events happened within the tightly linked X-STR clusters, which span<1.0 Mb; b) significantly linked marker pairs were observed with the LOD (logarithm of the odds) scores > 2.0 (2.0104 to 54.8316); c) the average mutation rate of the 38 X-STR loci was 1.32 × 10^-3 per meiosis in the Chinese Han population, with DXS10135 and DXS8377 presenting notably high mutation rate (6.5 × 10^-3). Our results confirmed that meiotic recombination was not a simple function of physical distance, so that whether recombination occurred at the closely clustered X-STRs or not should be assumed cautiously considering the stability of haplotypes in inheritance process for kinship analysis. This study supplemented the existing database and laid an experimental foundation for the future study on genetic characteristics, recombination, and mutation of the X-STRs.

Extended population genetic analysis of 12 X-STRs - Exemplified using a Norwegian population sample

The use of X-chromosomal markers to resolve questions of relatedness has experienced a significant increase during the last years in forensic genetics. Perhaps primarily due to the emergence of commercial kits, but equally important due to an increased awareness of the utility of those markers. The X-chromosomal inheritance pattern entails that some cases, for instance paternal half-sisters, can potentially be resolved using a few X-chromosomal markers alone. For the statistical assessment in kinship cases it is of importance to have relevant population frequency data. In the present study 631 unrelated males from a Norwegian population sample are analyzed. The resulting haplotypes are compared to previously studied population samples and a deeper analysis of the linkage disequilibrium (LD) structure is conducted. We demonstrate that the power to detect LD will be low when few males, say below 300, are analyzed. We use entropy to describe the degree of LD between multiallelic loci and describe how this measure varies between different studied populations. Large population frequency databases have been recommended when using X-chromosomal markers, and we show that by combining reference databases from genetically similar populations, more precise haplotype frequency estimates can be obtained for rare haplotypes which improves the statistical assessment of the weight of evidence. In addition, we promote the use of simulations to assess the utility of STR markers in contrast to standard forensic parameters. Specifically we perform extensive simulations on cases where X-chromosomal markers are important and illustrate how the results can be used to infer the information gained from these markers.

Genetic Structure and Forensic Feature of 38 X-Chromosome InDels in the Henan Han Chinese Population

Insertion/deletion (InDel) polymorphisms, as ideal forensic markers, show useful characteristics of both SNPs and STRs, such as low mutation rate, short amplicon size and general applicability of genotyping platform, and have been used in human identification, population genetics and biogeographic research in recent years. X-chromosome genetic markers are significant in population genetic studies and indispensable complements in some complex forensic cases. However, the population genetic studies of X-chromosome InDel polymorphisms (X-InDels) still need to be explored. In this study, the forensic utility of a novel panel including 38 X-InDel markers was evaluated in a sample of Han population from Henan province in China. It is observed that the heterozygosities ranged from 0.0054 to 0.6133, and the combined discrimination power was 1-9.18 × 10^-17 for males and 1-7.22 × 10^-12 for females respectively. The mean exclusion chance in trios and duos were 0.999999319 and 0.999802969 respectively. Multiple biostatistics methods, such as principal component analysis, genetic distances analysis, phylogenetic reconstruction, and structure analysis was used to reveal the genetic relationships among the studied Henan Han group and other 26 reference groups from 1,000 Genomes Project. As expected, the Henan Han population was clustered with East Asian populations, and the most intimate genetic relationships existed in three Han Chinese populations from Henan, Beijing and South China, and showed significant differences compared with other continental groups. These results confirmed the suitability of the 38 X-InDel markers both in individual identification and parentage testing in Han Chinese population, and simultaneously showed the potential application in population genetics.

Identification and Characterization of Nine Novel X-Chromosomal Short Tandem Repeats on Xp21.1, Xq21.31, and Xq23 Regions

The application of X-chromosomal short tandem repeats (X-STRs) has been recognized as a powerful tool in complex kinship testing. To support further development of X-STR analysis in forensic use, we identified nine novel X-STRs, which could be clustered into three linkage groups on Xp21.1, Xq21.31, and Xq23. A multiplex PCR system was built based on the electrophoresis. A total of 198 unrelated Shanghai Han samples along with 168 samples from 43 families was collected to investigate the genetic polymorphism and forensic parameters of the nine loci. Allele numbers ranged from 5 to 12, and amplicon sizes ranged from 146 to 477 bp. The multiplex showed high values for the combined power of discrimination (0.99997977 in males and 0.99999999 in females) and combined mean exclusion chances (0.99997918 and 0.99997821 in trios, 0.99984939 in duos, and 0.99984200 in deficiency cases). The linkage between all pairs of loci was estimated via Kosambi mapping function and linkage disequilibrium test, and further investigated through the family study. The data from 43 families strongly demonstrated an independent transmission between LGs and a tight linkage among loci within the same LG. All these results support that the newly described X-STRs and the multiplex system are highly promising for further forensic use.

X-chromosomal STRs for genetic composition analysis of Guizhou Dong group and its phylogenetic relationships with other reference populations

BACKGROUND

X-chromosomes show a specific genetic mode, which makes genetic markers on the X chromosome play crucial roles in forensic research and human evolution. Dong group, one of 55 minority groups in China, live in Guizhou, Guangxi and Hunan provinces. Even though some genetic data of Y chromosomal short tandem repeats (STRs) and autosomal insertion/deletion polymorphism (InDels) in Dong groups have been reported, there is little research about X-STRs in the Dong group.

AIM

Purposes of this study are to investigate allelic distributions and forensic statistical parameters of 19 X-STRs in the Guizhou Dong group, and explore the genetic composition of the Guizhou Dong group and its phylogenetic relationships with other reference populations.

SUBJECTS AND METHODS

507 Dongs (272 males and 235 females) living in Guizhou province were typed using the AGCU X19 STR kit. Allelic frequencies and forensic parameters of 19 X-STRs in the Guizhou Dong group were calculated. Population genetic analyses of Guizhou Dong and other 17 reference populations were conducted using D_A genetic distances, phylogenetic tree, principal component analysis and multidimensional scaling.

RESULTS

A total of 230 alleles of 19 X-STRs were identified in all Dongs. The frequencies of 19 loci ranged from 0.0013 to 0.6838. Cumulative power of discrimination in males (PDM), Cumulative power of discrimination in females (PDF), four different kinds of mean exclusion chance (MEC_Kruger, MEC_Kishida, MEC_Desmarais and MEC_Desmarais_du) values of 19 X-STRs in all individuals were 0.999999999999761, 0.9999999999999999999993951, 0.999999964841617, 0.999999999997261, 0.999999999997297 and 0.999999993623172, respectively. Besides, genetic polymorphisms of seven linkage clusters ranged from 0.9381 to 0.9963. In addition, these seven groups showed high polymorphism information content (PIC), PDM, PDF, MEC_Kruger, MEC_Kishida, MEC_Desmarais and MEC_Desmarais_duo values. Population genetic analyses of Guizhou Dong and other 17 reference populations showed that the Guizhou Dong group had close genetic relationships with surrounding Tai-Kadai-speaking, Hmong-Mien-speaking and Han groups.

CONCLUSION

Nineteen X-STRs displayed high genetic diversities and could be employed for forensic personal identification and paternity analysis in the Guizhou Dong group. Close genetic affinities between Guizhou Dong and surrounding populations were observed based on the 19 X-STRs in 17 reference populations.

Genetic diversity and forensic parameters of 12 X-STR included in Argus X-12® marker panel in the population of the Russian Federation

BACKGROUND

X-chromosome specific short tandem repeats (X-STR) are indispensable for parentage analysis, kinship determination and forensic casework.

AIM

To determine allelic frequencies and forensic parameters of the 12 X-STR markers from the Investigator^® Argus X-12^® kit panel for the population of the Russian Federation.

SUBJECTS AND METHODS

We analysed 803 unrelated individuals from 58 localities across the Russian Federation. Intra-population genetic diversity was evaluated and comparison of the Russian population with 19 geographically distant populations performed.

RESULTS

Heterozygosity values across all the loci ranged from 0.685 for DXS7423 to 0.939 for DXS10135. Deviations from the Hardy-Weinberg equilibrium were observed for DXS10074 (p < 0.05) and DXS10146 (p < 0.01). The value for power of discrimination across all the loci in males was 0.9999999996, while in females it equalled 0.9999999999. Combined mean exclusion chances MEC_Kruger, MEC_Kishida, MEC_D-trio, and MEC_D-duo were 0.9999988168, 0.9999999983, 0.9999999983, and 0.9999995797, respectively. Phylogenetic analysis indicated small genetic differences between the Russian population and the populations of neighbouring Lithuania, Belarus and the Slavic-speaking countries (Czech Republic, Serbia and Croatia).

CONCLUSIONS

This paper is the first report of forensically important parameters and allele frequencies for the 12 X-STR loci included in Argus X-12^® marker system in the population of the Russian Federation.

A reference database of forensic autosomal and gonosomal STR markers in the Tigray population of Ethiopia

Allele frequencies of 21 autosomal STR markers (AmpF/STR GlobalFiler) and haplotype frequencies of 27 Y- and 12 X-STR markers (AmpF/STR YFiler Plus and Investigator Argus X-12, respectively) were investigated in the Tigray population of Ethiopia, representing the main population group in the Tigray regional state of Ethiopia and neighboring Eritrea. For autosomal STR allele frequencies, the average random match probability in the Tigray sample was 2.1 × 10^-27. The average locus by locus F_ST distance calculated comparing autosomal STR allele frequencies from Tigray and from a broad regional reference dataset currently available for the Horn of Africa was 0.003. The Tigray male sample displayed high Y-STR diversity, with complete individualization of haplotypes using the AmpF/STR YFiler Plus panel. Analysis of molecular variance did not detect significant heterogeneity between Y-STR haplotypes observed in the present study and those previously reported in the literature for other Tigray population samples from Ethiopia and Eritrea. Study of the X-STR landscape in Tigray evidenced several distinctive features including: the molecular characterization of a novel null allele at locus DXS10146 with frequency > 1%; allele dependency between loci within linkage groups I and III; significant differences in haplotype distribution compared to other Horn of Africa populations, that should be taken into account in kinship analysis. The collected data can be used as a reference STR database by local forensic genetics services and in genetic identification procedures of victims of human trafficking in the Mediterranean Sea, which frequently involve individuals originating from the Horn of Africa.

Development and Validation of a Forensic Multiplex System With 38 X-InDel Loci

In the present study, a novel multiplex system, AGCU X-InDel 38 kit, was designed to amplify 38 X-InDel markers and amelogenin in a single Polymerase Chain Reaction (PCR). To demonstrate the suitability and efficiency for forensic applications, a series of validation experiments were conducted, including sensitivity, species specificity, reproducibility, stability, case samples, balance of peak height, size precision, as well as allele frequency and forensic parameter analysis. The results showed that AGCU X-InDel 38 kit was capable to get full profiles even with 62.5 pg of template DNA, and full profiles can be obtained when hematin concentration ≤25 μmol/L, or hemoglobin concentration ≤50 μmol/L, showing good tolerance to six common inhibitors. Moreover, the analyzed case samples indicated that AGCU X-InDel 38 kit had better performance for degraded and trace DNA samples. The 200 unrelated males from Guangdong Han population showed that the combined PD_Male and PD_Female were both more than 0.999999999, and the combined MEC_Krüger, MEC_Kishida, and MEC_{Desmarais  Duo} were 0.999369481, 0.999999917, and 0.999941556, respectively. Robust discrimination capability of this novel multiplex system could be demonstrated through the high values of forensic parameters. In conclusion, AGCU X-InDel 38 kit is sensitive, precise, reproducible, and highly informative and could be used as a complementary tool for complex and challenging kinship cases.

Population genetic analysis of 12 X-chromosomal STRs in a Swiss sample

X-chromosomal STRs are a powerful tool to assess a broad variety of complex kinship scenarios. We introduce herewith the first Swiss X-STR dataset based on 1198 individuals (592 female, 606 male), characterized with the Qiagen Investigator® Argus X-12 QS multiplex kit. Anomalous allele patterns, allele and haplotype frequencies, and forensic and population genetic parameters are presented. We detected linkage disequilibrium within three out of the four designated linkage groups and no apparent intra-national population substructure. We compared the dataset to a global panel of X-STR datasets and it fits well in the European context, as expected.

Exploring the Western Mediterranean through X-chromosome

In this study, we investigate the forensic and population genetics properties of 21 X-chromosome markers (9 X-Alu insertions and 12 X-STRs) in a dataset composed of 716 individuals from 11 Western Mediterranean populations. The high values of combined forensic parameters indicate that this 21 X-loci panel can complement autosomal or uniparental markers in kinship analysis and complex deficient paternity testing in the populations studied. Population analyses revealed a lower differentiation between Western Mediterranean human groups for X-STRs than for X-Alu insertion polymorphisms. Moreover, X-chromosome markers suggest a sex-biased migration rate, confirming the predominance of patrilocality in this area.