Identification of extra alleles in DYS385a/b multi-allelic patterns

Y chromosome short tandem repeats (Y-STRs) are widely used in forensic DNA analysis. Y-STRs usually genotyped as a monoallelic pattern, or a diallelic pattern at some double-copy loci. Abnormal genotypes with three or four alleles have been reported at DYS385a/b, which is a double-copy locus. However, multi-allelic patterns with more than four alleles have not been reported at this locus. In this study, abnormal five-allelic patterns at DYS385a/b locus were observed in 2 out of 7760 unrelated males from Henan Province, detected by the HG19 + 14Y fluorescence detection kit; and abnormal six-allelic pattern was observed in 1 out of 4920 unrelated males from Guangdong Province, detected by the AGCU Data Y30 fluorescence kit. The genotypes of these abnormal samples were confirmed again by the Yfiler (R) Plus and PowerPlex (R) Y23 kits. In order to understand the genomic structure of the extra alleles at this locus, forward and reverse primers were designed to sequence the three samples. The results showed that the five-banded and six-banded pattern genotype did exist at DYS385a/b locus. These data enriched the knowledge about multi-allelic patterns at DYS385a/b locus, which allowed the use of DYS385a/b profile in forensic analysis, even with multi-allelic patterns.