Abstract:
In forensic science, DNA profiles are used to characterize individuals and associate suspects with crimes. Modern DNA profiles are constructed using microsatellite markers, short tandem repeats of sequences of 2-5 base pairs. One tool for evaluating evidence based on DNA profiles is the match probability. The match probability is the conditional probability that a random person would have the profile of interest given that the suspect has it and that these people are different members of the same subpopulation. One issue in evaluating the match probability is hidden population differentiation, which can induce coancestry among members of the same subpopulation. Forensic assessments of DNA profiles which ignore such coancestry typically overstate the strength of evidence against the suspect. Theory has been developed to account for coancestry when evaluating match probabilites. Assumptions include a steady-state population of constant size, and a recurrent mutation model that may be unrealistic for microsatellite markers. We use a coalescent to investigate the robustness of the theory to a generalized stepwise model of microsatellite mutation, in growing rather than constant-sized populations. Demographic parameters are chosen to reflect historical human population estimates. Simulations demonstrate that, even when coancestry is taken into account, the probability of a matching profile can still be underestimated for common genotypes.
tr101.pdf