Investigative Genetic Genealogy from Highly Mixed Samples

Investigative genetic genealogy (IGG) has emerged as a powerful new tool to help identify DNA samples in law enforcement and medical examiner investigations, resulting in hundreds of identifications in cases that otherwise may never have been solved. A crucial component of successful IGG work is the genome-wide single nucleotide polymorphism (SNP) profile developed from a forensic sample and uploaded to GG databases. Errors in the SNP profile can result in the loss of GG matches or even the addition of false matches. One of the most challenging sample types to work with is high-level mixtures, where the person-of-interest represents 60% or less of the DNA present in the sample. Such samples are common in violent crimes, especially those with a sexual component. Uploading data from a highly mixed sample to a GG database results in a match list that is essentially unworkable due to the vast number of spurious matches. However, given data from one known contributor (usually the victim), it is possible for a highly skilled bioinformatician to accurately reconstruct the genotypes of the person-of-interest, upload the deconvoluted profile to GG databases, and obtain workable match results that an expert genetic genealogist can use for a GG investigation. This talk will go through 5 cases with highly mixed samples that resulted in a confirmed identification. We will show the SNP data and match results before and after deconvolution and demonstrate that these identifications could not have been made without high-quality mixture deconvolution.