Complex DNA profiles present challenges to interpretation. Traditional methods, such as Combined Probability of Inclusion (CPI) and Random Match Probability (RMP), struggle to handle these profiles and are being superseded by probabilistic genotyping methods. All of these methods are likelihood ratio (LR)-based. Lack of familiarity with LRs leads to unnecessary concern about the transition from traditional method to probabilistic genotyping methods. Key issues involve proposition setting, the mathematical structure of LRs, and reporting and explaining them in court.

Modern multiplexes have considerable discriminating power. This means that any remaining probability is focused on relatives. There is a general move in the U.S. to consider a possible future move to methods that directly accommodate relatedness in the population.

This module:

• Describes forensic STR markers: mutation process, genotyping technology, and electropherogram artifacts particularly new considerations for back, forward, double back stutter and exotics.
• Reviews principles of population genetics, and measurement of relatedness.
• Covers general principles of evidence evaluation using LRs, computing LRs for identification using presence/absence of autosomal STR genotypes and for mitochondrial and Y-chromosome markers.
• Addresses the complications of mixture interpretation when the queried contributor is a relative of true contributor.
• Describes the consequences of database searches.
• Discusses briefly probabilistic interpretation of STR profiles.
• Provides information about new molecular techniques for human identification.