Assessing the forensic value of DNA evidence from Y chromosomes and mitogenomes

TL;DR

This paper reviews how Y chromosome and mitochondrial DNA profiles are used as forensic evidence, emphasizing the importance of mutation rates and relatedness in interpreting their significance and the limitations of current evaluation methods.

Contribution

It provides a comprehensive analysis of the challenges in evaluating lineage marker DNA evidence, highlighting the impact of mutation rates and relatedness on forensic interpretation.

Findings

Higher mutation rates reduce profile frequency but increase relatedness among matches.

Relatedness complicates the assessment of true source probability in forensic cases.

Many current evaluation methods do not adequately account for relatedness effects.

Abstract

Y-chromosomal and mitochondrial DNA profiles have been used as evidence in courts for decades, yet the problem of evaluating the weight of evidence has not been adequately resolved. Both are lineage markers (inherited from just one parent), which presents different interpretation challenges compared with standard autosomal DNA profiles (inherited from both parents), for which recombination increases profile diversity and weakens the effects of relatedness. We review approaches to the evaluation of lineage marker profiles for forensic identification, focussing on the key roles of profile mutation rate and relatedness. Higher mutation rates imply fewer individuals matching the profile of an alleged contributor, but they will be more closely related. This makes it challenging to evaluate the possibility that one of these matching individuals could be the true source, because relatedness may make them more plausible alternative contributors than less-related individuals, and they may not be well mixed in the population. These issues reduce the usefulness of profile databases drawn from a broad population: the larger the population, the lower the profile relative frequency because of lower relatedness with the alleged contributor. Many evaluation methods do not adequately take account of relatedness, but its effects have become more pronounced with the latest generation of high-mutation-rate Y profiles.