Genetic Polymorphisms Of Four STR Loci On Chromosome X In Chongqing Han Population

Background and objective:Microsatellite DNA, also named short tandem repeats (STR) or simple sequence repeats (SSRs), are the repeats which have 2～6bp repeat units. As one of the widest length polymorphic genetic markers, they are now widely used in forensic hematogenetics. Because the short tandem repeat locus are widely dispersed in human genome, typing simply, rapid, repetitive and highly sensitive, they became the main direction of the individual identification and paternity testing in domestic and international forensic medicine. Autosomal and Y chromosome STR loci have been widely studied and applied currently, but the X chromosome STR loci can be used in forensic paternity test, and some special cases of personal identification for their unique genetic characters. To investigate the genetic polymorphism and discuss the significance in forensic medicine of the Han population in Chongqing, we chose the four STR locus (DXS7132,DXS6789,HPRTB,DXS8378) on X chromosome in unrelated individuals in Han population in Chongqing. Methods: EDTA-blood specimens were collected from 211 unrelated individuals (120 females, 91 males) in Chongqing Han population. The genomic DNA was extracted by chelex-100 method and stored in -20℃. The four locus were amplified with PCR. The fragments were amplified in each 20ul reaction volume with different parameters. After 30 to 35 cycles, the mixture of PCR products with loading buffer were typed by 6% polyacrylamide gel electrophoresis at 300V, for 3h, followed by silver stain. Then allele frequencies, and genotype frequencies were obtained by a direct calculation; test of Hardy-Weinberg equilibrium for female genotype data and comparing of allele frequencies between male and female population, were performed by X 2 test; Heterozygosity (H), probability of matching (Pm), probability of discrimination power (DP), exclusion probability of paternity (PE) and polymorphism information content (PIC) were tested by Powerstates1.2 of Promega company and Exel.Results: Among 120 female and 91 male unrelated individuals from Chongqing Han population, 7 alleles were found in the DXS7132, named 11～17; DXS6789 exhibited 10 alleles named 15～24; HPRTB detected 9 alleles named 9～17; 6 alleles named 9～14 in DXS8378. X 2 testing showed that there were no difference between male and female, and the genotype frequencies in females did not depart from Hardy—Weinberg equilibrium (P>0.05). Discrimination power for females of each locus were 0.910,0.955,0.939,0.806, probability of exclusion were 0.646,0.615,0.543,0.367 respectively of the four locus DXS7132, DXS6789, HPRTB, DXS8378. Then comparing the allele frequencies with the different regions and different ethnic groups through articles found that there is a certain difference.Conclusions: These results were first provided the polymorphic data at DXS7132, DXS6789, HPRTB, DXS8378 locus in Chongqing Han population. These four locus all shows high polymorphism, good discriminating power and high excluding chance of paternity, and they are different from the other groups. So the data we received could help to construct the DNA database population genetics database, they are valuable for the research of the anthropological genetics and the individual identification of forensic Medicine and paternity testing in Chongqing Han population.