Estimating Individual Contributions to Complex DNA SNP Mixtures

Abstract

A B S T R A C T Mixture analysis and deconvolution methods can identify both known and unknown individuals contributing to DNA mixtures. These methods may not identify all DNA contributors with the remaining fraction of the mixture being contributed by one or more unknown individuals. The proportion of DNA contributed by individuals to a forensic sample can be estimated using their quantified mixture alleles. For short tandem repeats (STRs), methods to estimate individual contribution concentrations compare capillary electrophoresis peak heights and or peak areas within a mixture. For single nucleotide polymorphisms (SNPs), the major:minor allele ratios or counts, unique to each contributor, can be compared to estimate contributor proportion within the mixture. This article introduces three approaches (mean, median, and slope methods) for estimating individual DNA contributions to forensic mixtures for high throughput sequencing (HTS)/massively parallel sequencing (MPS) SNP panels.

Using FastID to analyze complex SNP mixtures from indoor dust

“…While the main application of such probabilistic genotyping software has been for STR mixtures, studies have also highlighted their applicability with SNP mixtures (e.g., [41,42]). Using software such as FastID [43] and EuroForMix [44], SNP alleles for minor contributors (up to 1:400) can be accurately assigned (99.9%) [45,46], and profiles for complex mixtures (i.e., <10 contributors) identified [46].…”

“…While the main application of such probabilistic genotyping software has been for STR mixtures, studies have also highlighted their applicability with SNP mixtures (e.g., [41,42]). Using software such as FastID [43] and EuroForMix [44], SNP alleles for minor contributors (up to 1:400) can be accurately assigned (99.9%) [45,46], and profiles for complex mixtures (i.e., <10 contributors) identified [46]. This study examined the (a) utility of indoor dust as source of human DNA, (b) recovery of forensically relevant SNPs from indoor dust samples using the Precision ID Identity and Ancestry Panels (Thermo Fisher Scientific), and (c) practicality of FastID for the detection of both known and unknown occupant alleles in mixed dust samples.…”