Likelihood ratio development for mixed Y-STR profiles. (July 2018) - Taylor, Duncan
Highlights: We introduce a new method to calculate likelihood ratios for Y-STR data, termed the haplotype centred (HC) LR. The HC method is able to be applied to mixed Y-STR profiles in a locus by locus manner. We derive the formula for the HC method using standard population models. We demonstrate the use of the HC method on two to four person mixed YSTR profiles. Abstract: In this paper we introduce a new likelihood ratio method for evaluating mixed Y-STR profiles that is based on the premise that, given a haplotype has been seen in the person of interest, the most likely source of a second haplotype, matching at all or most loci, is in an individual with a recent common ancestor. We have called the new method the "Haplotype centred" (HC) method for likelihood ratio derivation. For single source, unambiguous haplotypes the HC method performs identically with the Kappa method proposed by Brenner. When attention is turned to mixtures we are required to assign a probability to many haplotypes seen neither in the database nor any person typed in the case. We derive a likelihood ratio formula in a way that allows a locus by locus approach. We demonstrate the application of the HC method on a series of Y-STR mixtures, originating from two to four individuals, in a manner that is still calculated locus-by-locus in nature.