Genetic Polymorphism Of Four X Chromosome STR Loci In Hebei Han Population

Objective: As one of the widest length polymorphic genetic markers, short tandem repeat (STR), also named microsatellite DNA or simple sequence repeats (SSRs), are currently used in forensic hematogenetics. The short tandem repeat loci are widely dispersed in the human genome and have high sensitivity and discrimination power. The allele fragment length of STR locus is usually shorter than 400bp, so it is amplified easily and very suitable for antiquated, degradated and rotten materials. STR locus can be multiplex amplificated, so it is very useful for trace materials. Now autosomal and Y-chromosomal STRs are widely researched and applied, while the X-STR markers are not. Because X chromosome has the character that the male transmits his X chromosome only to his daughter(s), it can provide more information than the autosomal does, particularly in complex cases of kinship testing. For instance, the cases of deficiency paternity testing when the disputed child is a girl or the cases identified whether presumptive half-sister have the same genetic father without examination of the parents. To provide more information for the construction of X-STRs DNA database and a useful tool in paternity studies and other forensic case, the study observed the genetic polymorphisms of DXS6800 /DXS6797 / GATA172D05 / DXS986 4 loci in Hebei Han population.Methods:The genome DNA of unrelated individuals, the families and rotten materials were extracted with phenol-chloroform method and Chelex-100 method, respectively. DXS6800 /DXS6797 / GATA172D05 / DXS986 fragments were amplified, in each 20μl reaction volume with different parameters. After 28 cycles, allele fragments in different length could be obtained. The mixture of 3μl PCR products and 3μl denaturing formamide loading buffer was separated by 6% denatured polyacrylamide gel electrophoresis (6mol/L urea) at 200V, for 5h, followed by silver stain. Alleles were determined by comparing with allelic ladders which were made by ultracentrifugation method. Alleles were assigned according to the recommendations of the International Society of Forensic Genetics (ISFG) Commission after sequencing.Results: The genetics parameters of the 4 loci: In the 150 male and 150 female unrelated individuals of Hebei Han population, 6 alleles were found in the DXS6800 locus, 6 alleles in the DXS6797, 6 alleles in the GATA172D05, 7 alleles in the DXS986. X2 testing showed that there were no difference between male and female (P>0.05), so the data were pooled to estimate the total allele frequencies of each STR locus. The probability of discrimination power (PD) of DXS6800 /DXS6797 /GATA172D05 /DXS986 for females was 0.9087, 0.9777, 0.9271 and 0.9627 respectively. The excluding probability of paternity were 0.7117, 0.8773, 0.7619 and 0.8399, respectively. The polymorphism information content (PIC) for all the individuals was 0.8086, 0.8279, 0.8466 and 0.8507.The male haplotype frequencies of the 4 loci: 150 haplo -types have been found among 138 males. The gene diversity(GD), the probability of discrimination power (PD) and the female excluding probability of paternity (PE) were 0.9986, 0.9986 and 0.9993 respectively.The stability of heredity of the 4 loci: Family analysis of 8 individuals from 4 families at the 4 loci demonstrated that the father can transmit his alleles stably to his daughter(s), which is consistent with Mendel's law.The identity character of the 4 loci: Rotten materials of different tissues in the same cadaver were analyzed to result that each locus has the same allele. The 4 loci are all available to the standards of the forensic DNA analysis.Conclusions: The findings first provided the polymorphic data at DXS6800 /DXS6797 /GATA172D05 /DXS986 loci in Hebei Han population. The high polymorphism of the 4 loci would provide a potential tool for individual identification and paternity testing in Hebei Han population.