The Use of MSY1 Locus in the Investigation of Mixed Samples: A method to reduce the problems associated with interpreting mixed DNA profiles

The resolution and interpretation without ambiguity of mixed DNA profiles using diploid loci is often difficult. Profiling DNA from forensic mixtures can be achieved through autosomal multiplexes, but the interpretation can be impeded in complex mixtures due to the inability of the system to discriminate between the multiple male contributors. Besides using Y-chromosomal STRs, the highly polymorphic haploid MSY1 locus on the human Ychromosome has potential application in the resolution of mixed biological samples where male and female cells are present together, even without carrying out the differential extraction procedure. In this study, an alternative method to characterise the structural diversity at the MSY1 locus was developed. DNA mixtures from simulated and real samples were used to challenge the resolution and interpretation of multiple-source samples. A highly diverse mixed male DNA sample and a real forensic casework stain were also analysed. The MSY1 products (between 2-3kb) were first amplified under high stringency using a modified flanking primer pair, and then amplified in a semi-nested PCR using a flank plus a junction primer. Three junction primers were used to generate products between the flank and the targeted junctions of repeat type 1 and 3, repeat type 3 and 1 as well as repeat type 3 and 4. The resulting length polymorphisms are presented and discussed.