Analysis of Forensic Mixtures

Chapter 3 discusses the challenges posed by forensic DNA specimens with multiple contributors. These mixed samples from two or more individuals are common in forensic cases, and comparing the profile of a suspect sample with the complex profile of the mixture is one of the most difficult problems in forensic DNA analysis. Mixtures with limited amounts of DNA create particular challenges for interpretation due to the possibility of missing data. The chapter discusses issues with the interpretation of mixed STR profiles, such as “stutter bands” and “allele drop-out.” It reviews specific cases and current approaches to deconvolution of the mixtures, including use of the recently developed software for probability-based statistical analysis of STR profiles and the potential of next generation sequencing. It also examines several statistical approaches to presenting the results of mixture analysis, such as the combined probability of inclusion and the likelihood ratio.