The analysis of short tandem repeat markers located on the Y chromosome is an established method in forensic casework analysis. Y chromosome markers are used to assist forensic investigations in rapid sexing of traces, for the identification and profiling of masked male DNA components in mixtures with an excess of female DNA, for tracing male lineages in relationship testing or for analysing the deep-rooting ancestry of unidentified corpses or unknown trace donors.
Usually, this method is applied in cases of male-on-female sexual assault, in which the victim’s DNA is in great excess and masked the male contribution. Y-STR analysis is able to detect the presence of minuscule amounts of male DNA of one or multiple donors and resulting genetic profiles can be compared to known reference samples.
The expert has to determine whether the Y-STR result of a trace is suitable for a biostatistical calculation in case of a match. Y-SNPs in combination with Y-STRs can infer the biogeographical origin of an unknown male person with comparably high precision due to the availability of a robust phylogenetic tree and large reference data collections.
Y-based ancestry prediction and familial searching can provide important investigative leads in crime cases without suspect. Judging the significance of a match depends upon the population frequency of the profile.
Y chromosomes are highly geographically structured and there is the further complication that all members of a patrilineage are expected to share Y haplotypes. The forensic community has established a large quality-assured and publicly accessible databases of Y-haplotypes to address these issues.