Exploring likelihood ratios assigned for siblings of the true mixture contributor as an alternate contributor

Abstract

Relatives tend to have more DNA in common than unrelated people. The closer the biological relationship, the higher the chance of alleles being identical by descent between the individuals. Therefore, when considering a mixed DNA profile, close relatives of the true contributor may not always be excluded as a possible contributor to a mixture due to allele sharing. In these situations, it might be more appropriate under the alternate proposition to consider that the DNA could have originated from a relative of the person of interest rather than an unrelated individual. The probabilistic genotyping software STRmix™ automatically provides LRs considering close biological relatives as alternate sources of the DNA. In this paper, we investigate the support for siblings of the true contributor to a mixture (who are not present in the mixture themselves). We interpret the mixtures and assign LRs using STRmix™ and investigate whether the resulting LRs could be used to indicate whether the true contributor could be a sibling of the POI. Most siblings will have one or more alleles that are not observed in the mixture profile. Support for siblings to have contributed can only occur when allelic dropout is a possibility at the loci where the siblings have alleles that are not observed in the profile. In these data, that was only observed in components with assigned template of 588 rfu or less.

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“…Such experiments would be more challenging for probabilistic genotyping methods. Initial analyses, though without comparing different models, have already been performed [12].…”

Single cell genomics applications in forensic science: Current state and future directions

“…Some complex familial mixtures comprising several first-degree relative donors can yield false inclusions and exclusions using standard bulk STR mixture analysis. 34 , 120 However, scDNA analysis conducted in some of these complex familial mixtures can prevent the false inclusion of non-donor relatives. 102 …”

An Investigation into Compound Likelihood Ratios for Forensic DNA Mixtures

“…In this case, it is prudent to test whether these POI could explain the profile when considered together. This could be undertaken using a compound proposition pair, defined as one where more than one POI within H p is replaced with unknown donors in H a ([ 8 ], hereafter the ASB (American Standards Board) draft standard and see also [ 9 , 10 ]).…”