The Detection Of15Frequently Used Forensic STRs And Their Application To The Inference Of Population Genetic Distance

Background and purposeShort Tandem Repeats (STR) is a kind of DNA sequences that is generally formed by the repeat of a core sequence with two or more nucleotides. The fragment length of the repeat region is generally less than400bp, the core repeat unit is2～6bp and repetitions can be10～60times. Different STRs have different core sequences, and the same STRs have different repetitions among persons. These lead to the individual differences and form a genetic polymorphism. So STRs are widely used in individual identification and paternity testing. Because STRs have a wide distribution, high polymorphism, Mendelian inheritance style, they have also become an effective tool to infer the genetic distance among different ethnic groups.Kazakh is Kazakhstan’s main ethnic group, and it is one of the minorities in China. The population of Chinese Kazakh is about17million. In China, this nationality mainly line in Xinjiang Uygur Autonomous Region, the Hi Kazakh Autonomous Prefecture, Mori Kazak Autonomous County, Barkol Kazak Autonomous County and Aksay Kazak Autonomous County in Gansu Province. Their native language is Kazakh, and the character of Kazakh this is based on Arabic alphabet. According to their inheritance linkage, this ethnic group belongs to a mixed type, which is among the North Asian type of the Mongoloid, the white race and the India Mediterranean race. It belongs to the Turkic tribe, classified by the linguisticians.Some Kazakh peoples is still living a nomadic way of life, with no fixed residential areas. Their areas are far more remote, with inconvenient transportation and less developed economic status. Due to these reasons, the15frequently used forensic STR data of the Kazakh population in China is not reported until we set out to test their samples at the end of2010. Since my supervisor have the opportunity to obtain Xinjiang Kazak blood smaples from his Xinjiang connections, we decide to test these blood samples for the data of the commonly used15forensic STR loci.Searching through the network databases or peer-reviewed journals, this study has collected the STR loci frequency data in other ethnic groups from all provinces in China. To explore the genetic relationship between the different Chinese nationalities, a phylogenetic tree based on the calculation of genetic distance among40different ethnic groups will be tried to be built.MethodsDNA samples were extracted from the peripheral blood of100Xinjiang Kazakh by the method of phenol-chloroform extraction. Using the Identifier kit to finish the fluorescence-PCR amplification, then a capillary electrophoresis for PCR products were done on3130DNA genetic analyzer. Finally, we accomplished the polymorphism investigation of the15STR loci among100healthy cases of Kazakh. Through the public databases or peer-reviewed journals, STR loci frequency data of other ethnic groups was collected from all provinces in China. After gathered the data from this study and references, we calculated the frequencies of9commonly used forensic STR loci (D13S317, D18S51, D21S11, D3S1358, D5S818, D7S820, D8S1179, FGA, vWA) in China’s40ethnic groups. The genetic distance was calculated by the Phylip3.69statistical package, and the phylogenetic trees was constructed by the Neighbor-joining method to study the genetic relationships between the various ethnic groups.Results15STR loci in100cases of Xinjiang Kazakh were detected, respectively, there are10,15,8,10,6,6,7,6,12,11,8,6,12,7,10alleles were found; the range of these gene frequencies distribute in0.01～0.25,0.005～0.275,0.01～0.225,0.015～0.33,0.01～0.335,0.01～0.285,0.015～0.24,0.025-0.265,0.015～0.205,0.015～0.29,0.02～0.26,0.01～0.595,0.005～0.255,0.025～0.365and0.005～0.205.Nine STRs loci gene frequency data of all40ethnic groups were compared to calculate the genetic distance, and a phylogenetic tree was constructed using the Neighbor-joining method based on genetic distances of40populations. In the lower half of the phylogenetic tree, the Xinjiang Uygur is the nearest to Mongolians, and then come near to the Kazak, to Inner Mongolia, to Daur, to Hans in Tianjin, to Hui in Qinghai, and then they go to Tibetans in Qinghai, Tibetans in Tibet, to Lhoba in Tibet, to Shes in Zhejiang subcategories for a convergence, then Shaanxi Hans, Yunnan Bais, Tianjin Koreans, Hunan Tujias, Shandong Hans, Jiangsu Hans. And then join Hans in Hebei, Hans in Inner Mongolia and Hans in Henan, Hans in Liaoning, constituting the entire population of North Chinese. On the upper half of the phylogenetic tree, the Maonan of Guangxi and the Jing of Guangxi come together first, the join the Guangxi Miao, Guangxi Mulao; then the Yaos in Guangxi and Lis in Hainan come in for a convergence. Next come the Yaos in Guangxi, Hans in Hainan. The Dongs in Guangxi, Zhuangs in Guangxi. Then Hans in Guangxi, Hans in Guangdong join, together with the Hans in Sichuan, Hans in Fujian, Hans in Hubei and Tujias in Chongqing, constituting the southern Chinese population. While Anhui Hans and Zhejiang Hans become a transition between the Southern Han Chinese population and Northern Hans.Conclusion The data of15STR loci in100cases of Kazakh obtained in this study will not only provide basic information for future’s forensic applications such as individual identification, paternity testing, but also provide an important basis for the study of this ethnic’s genetic characteristics, the analysis on its evolution and its origin, and the genetic relationships among different ethnic groups,and unique disease spectrum caused by ethnic genetic defects.There are genetic differences between the Northern and the Southern Chinese population.There are genetic differences between the Han population and the minorities.