Y Chromosome Short Tandem Repeats Typing

The application of the Y chromosome short tandem repeats (Y-STR) in forensic field and lineage studies has been dramatically growing in the last few decades. In forensic cases, when male–female mixtures cannot be resolved using autosomal STR multiplexes kits, the application of Y-STR profiling will add a beneficial value by producing the male Y-STR haplotype. In forensic application, Y-STR is mostly used in sexual assault cases, paternity testing, familial searching, and male disaster victim identification (DVI). Assigning a weight to a haplotype match between evidence and reference samples is essential to make it admissible in court to help achieving justice. Because of the nature of the inheritance pattern of Y chromosome through male lineages, all loci located on Y chromosome are considered as one locus. Consequently, to assign the weight, a relevant Y-STR haplotype database should be employed to estimate the rarity of a Y-STR haplotype. This chapter explains the concept and history of Y-STR typing and its application for forensic investigation purposes. It explains all commercially available Y-STR multiplex kits such as PowerPlex® Y23 and Yfiler® Plus. Also, an illustration of in-house-developed multiplex kits for rapidly mutating Y-STRs is also presented. The discrimination capacity between male individuals, both relatives and non-relatives, and also haplotype diversity of these kits are illustrated briefly in this chapter. The interpretation guidelines of different types of loci, single-allelic and multi-allelic, are explained as per the international standard guidelines recommended by SWGDAM and ISFG. In addition, the two main Y-STR databases, YHRD and US Y-STR, are discussed along with other databases which are used for genealogy studies. Moreover, the utilization of these databases to estimate the rarity of Y-STR haplotypes and its involved statistical uncertainties following different approaches has been discussed.