The six-dye GlobalFiler™ Express PCR amplification kit incorporates 21 commonly used autosomal short tandem repeat (STR) loci and three gender determination loci. In this study, we analyzed the GlobalFiler STR loci on 748 unrelated individuals from a Chinese Kazakh population of Xinjiang, China. No significant deviations from Hardy-Weinberg equilibrium and linkage disequilibrium were observed within and between 21 autosomal STR loci. SE33 showed the greatest power of discrimination in Kazakh population. The combined power of discrimination of Kazakh was 99.999999999999999999999996797 %. No significant differences of allele frequencies were observed between Kazakh and Uyghur at all 15 tested STR loci, as well as Mongolian. Significant differences were only observed between Kazakh and the other Chinese populations at TH01. Multiple STR loci showed significant differences between Kazakh and Arab, as well as South Portuguese. The multidimensional scaling plot (MDS) plot and neighbor-joining tree also showed Kazakh is genetically close to Uyghur.
The introduction of a set of highly polymorphic short tandem repeat (STR) loci for human individual identification (HID) has proven to be successful in forensic investigations . A total of 24 autosomal STR loci were commonly used in forensics , which were embedded in several multiplex amplification kits. Recently, the six-dye GlobalFiler™ Express PCR Amplification kit were developed by Thermo Fisher Scientific company , which includes 21 autosomal STRs of above 24 markers and three gender determination loci (Amelogenin, Yindel, and DYS391). The autosomal STR loci in GlobalFiler kit are D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, VWA, TPOX, D18S51, D5S818, FGA, D12S391, D1S1656, D2S441, D10S1248, D22S1045, and SE33. Some previous studies have shown that the GlobalFiler kit can support reliable DNA typing results and enhanced discrimination power [4, 5], and a few population data of the GlobalFiler STRs were recently released [6, 7].
Kazakh is one of ethnic populations of Xinjiang Autonomous Region in northwest China. According to the 2010 census, the population of Kazakh had reached 1.462 million, who mainly lives in the Ili Kazak Autonomous Prefecture, Mori Kazak Autonomous County, and Barkol Kazak Autonomous County . To evaluate the performance of the GlobalFiler kit on a Chinese Kazakh population, here, we typed the GlobalFiler STR loci in 748 unrelated Kazakh samples who were collected from Xinjiang. Peripheral blood samples were collected from these individuals after acquiring their informed consent. Amplification of 24 loci were performed using GlobalFiler™ Express kit (Thermo Fisher Scientific company, Carlsbad, USA) in the GeneAmp PCR System 9700 (Thermo Fisher Scientific company) according to manufacturer’s recommendation. PCR products were separated by capillary electrophoresis in an ABI PRISM 3730xL genetic analyzer (Thermo Fisher Scientific company). The GeneMapper® ID-X software v1.4 (Thermo Fisher Scientific company) was used for genotype assignment. DNA typing and assignment of nomenclature were based on the ISFG recommendations [9, 10].
The allele frequencies were estimated from corresponding genotype counts. The exact tests of Hardy-Weinberg equilibrium (HWE) and linkage disequilibrium (LD) were performed using Arlequin v3.5 , and the observed heterozygosity (Ho) and expected heterozygosity (He) were also estimated. Match probability (MP), power of discrimination (PD), and power of exclusion (PE) were estimated using Modified-Powerstats . The exact test of population differentiation was performed between Kazakh of the present study and the other populations using Arlequin v3.5 . We also estimated pairwise Fst as described by Weir and Hill  to measure the genetic distance between populations. Results were visualized by multidimensional scaling plot (MDS) using R v3.1.2 (http://www.r-project.org) and neighbor-joining tree was construced using Mega 6 software .
To evaluate whether random match probability can be estimated using simple product role , we performed HWE and LD test within and between STR loci in the GlobalFiler kit. No significant deviations from HWE were observed after Bonferroni correction (P > 0.002381) (see Table S1). We also found no significant deviations from LD between pairwise STR loci after Bonferroni correction (P > 0.0002381) (see Table S2). The results showed that match probability can be estimated in a Kazakh population by multiplying the allele frequencies within and across 21 STR loci.
The allele frequencies and forensic statistical parameters of 21 autosomal STR loci are shown in Table S1. Ho ranged from 0.6350 (TPOX) to 0.9398 (SE33), whereas He ranged from 0.6239 (TPOX) to 0.9461 (SE33). PD ranged from 0.7987 (TPOX) to 0.9932 (SE33), and PE ranged from 0.3350 (TPOX) to 0.8773 (SE33). The results showed that SE33 had the greatest power of discrimination in Kazakh population. The combined power of discrimination (CPD) was 99.999999999999999999999996797 %, and the combined power of exclusion (CPE) was 99.9999998683861 %. The combined match probability (CMP) was 3.203 × 10−26. Thus, the GlobalFiler kit has the greatest power of HID of the currently available commercial multiplex STR kits.
The exact test of population differentiation was performed between Kazakh of the present study and the other populations from earlier reports (Table S3). Overall, the allele frequency data of the 12 populations were obtained, including ten Chinese populations typed by different amplification kits , as well as the populations from South Portugal  and United Arab Emirates  who were both typed by the GlobalFiler kit. The Chinese populations include six Han populations from different areas (Jilin, Gansu, Qinghai, Shandong, Jiangsu, and Guangdong) and four ethnic groups (Tibetan, Dai, Mongolian, and Uyghur). After Bonferroni correction (P = 0.05/195 = 0.00026, 192 was the number of test), no significant differences were observed between Kazakh and Uyghur at all 15 tested STR loci, as well as Mongolian. These two populations have similar geographic distributions with Kazakh, especially Uyghur has been proven having a close genetic relationship with Kazakh in previous studies [8, 17]. In the comparison between Kazakh and the other Chinese populations, significant differences were only observed at TH01. The results showed that the frequencies of 15 GlobalFiler STR loci at least had no significant differences between Kazakh and the other Chinese populations, and the other six STR loci still remain tests in China while more data of GlobalFiler STRs are generated in the future.
We also performed exact test of population differentiation between Kazakh and the other two worldwide populations. Significant differences were observed between Kazakh and Arab from the United Arab Emirates, as well as South Portuguese populations at multiple STR loci. Among them, only the frequencies of CSF1PO, D3S1358, D8S1179, and FGA showed no significant differences. All six STR loci out of the AmpFlSTR Identifiler markers (D10S1248, D12S391, D1S1656, D22S1045, D2S441, and SE33) showed significant differences between Kazakh and the above two populations.
Unbiased Fst were estimated based on 15 shared STR loci among studied populations. As showed in Fig. 1, Kazakh is genetically close to Uyghur, and both of them show apparent separation of other Chinese populations and Arab, as well as South Portuguese. The same conclusion could have been observed in the neighbor-joining tree (Fig. 2). The results indicated that the Kazakh population may be mixed by the ancestral groups from Western and Eastern Eurasians.
In conclusion, we report the allele frequencies and forensic statistical parameters of the GlobalFiler STR loci in Chinese Kazakh population, which may serve as a forensic database reference of Chinese populations.
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This study was supported by grants from the National Science Foundation of China (31271338), Project of Chinese Ministry of Education (113022A) and the National High Technology Research and Development Program (2012AA021802).
Conflict of interest
The authors declare that they have no competing interests.
Honghua Zhang and Shuping Yang contributed equally to this work.
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Zhang, H., Yang, S., Guo, W. et al. Population genetic analysis of the GlobalFiler STR loci in 748 individuals from the Kazakh population of Xinjiang in northwest China. Int J Legal Med 130, 1187–1189 (2016). https://doi.org/10.1007/s00414-016-1319-2
- Short tandem repeat