Differential pattern of genetic variability at the DXYS156 locus on homologous regions of X and Y chromosomes in Indian population and its forensic implications

Sex determination is routinely performed in forensic casework using the amelogenin-based sex test. The human amelogenin gene resides on homologous regions of the sex chromosomes. However, a deletion in the AmelY locus may sometimes lead to gender misidentification. The pentanucleotide microsatellite DXYS156 maps to the pseudoautosomal region of both the sex chromosomes and helps in sex determination. This STR offers an advantage of being multi-allelic, with delimited and demographically restricted alleles for the X and Y chromosomes. Also, the Y-specific alleles can be discerned from their X chromosomal counterpart due to an adenine insertion in the (TAAAA) n repeat units of the STR. The present study examines the differential variation pattern at the X and Y locus of this STR in unrelated males from linguistically and geographically diverse populations of India. The study also attempts to undertake a comparison between the two sex-determining markers through validation studies. Two population samples and few validation samples which showed erroneous results for the amelogenin locus produced alleles specific to each of the sex chromosomes at the DXYS156 locus. The error rate for the amelogenin locus was observed to be 0.27% in case of the population samples and 0.5% in case of validation samples. Statistical parameters of forensic interest indicate that the DXYS156 locus is polymorphic and discriminating for the Indian population.