Abstract

Co-author: Taryn Hall (University of Washington)

Although the interpretation of DNA evidence has been discussed extensively, there are still areas where there remains debate on the best methods. One area is for profiles on the Y chromosome, where the lack of recombination suggests the locus-specific profiles are not independent. Although an examination of published data demonstrates that many of the loci do have independent profiles, there are sufficient dependencies that there seems little need to continue adding loci to increase discrimination: profiles matching at 30 loci are unlikely not to match at the 31st locus for example.

Purely statistical approaches break down in practice because most evidential profiles are not represented in profile databases. Observed profile frequencies offer little guide to the evidential strength of a Y-chromosome match. We have used both published and simulated data to evaluate various genetic models that serve as a basis for estimating match probabilities.

Y-chromosome lineages often cross geographic or ethnic population boundaries. Genetic models allow predictions of the probability that two men, one of whom is unknown, will share Y-chromosome profiles when they are members of the same or different populations.