Mixed Stains from Sexual Assault Cases: Autosomal or Y-chromosome Short Tandem Repeats?

We analyzed forensic DNA samples from four cases of sexual assault, using the Y-chromosome-specific human DNA markers and a panel of autosomal short tandem repeats (STRs). The presence of male contributionwas evaluated by the analysis of the Amelogenin locus. A panel of tetrameric Y-STR (DYS19, DYS390, DYS391, DYS392, DYS385, DYS389I and II) was used in further analysis of samples, increasing the efficiency of the forensic genetic analyses. Itwas possible to identify a partial or full Y-profile of the rapists in different DNA mixtures when genetic profile could not be detected by autosomal STRs. However, in the case ofmale/maleDNAmixture, only the victim’s Y-profile could be obtained because the DNA of the offenders was present in low amounts. When the mixture contained different male/male proportion of DNA, only the full profile of themajor component could be detected. In cases wheremale/female DNA mixed stains contained a sufficient amount of male DNA, the analysis of autosomal STRs was adequate enough to identify the full profile of the rapist. Our experience shows that the main advantage of the Y-STR approach is its ability to detect themale component in themixed stains when the DNA of themale contributor is present only in a very small amount.