Y-talks
A series of five talks on the forensic evaluation of Y-profile (and mtDNA) evidence.
Mikkel Meyer Andersen (Aalborg University, Denmark) Follow @mikldk
David Balding (University of Melbourne, Australia) Follow @djbalding
Last updated: Aug 6, 2021 (exactly one year since last update!).
Assessing the Forensic Value of DNA Evidence from Y Chromosomes and Mitogenomes
Abstract: Y chromosome 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). We review approaches to the evaluation of lineage marker profiles for forensic identification, focussing on the key roles of profile mutation rate and relatedness (extending beyond known relatives). 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 relatives may be plausible alternative contributors, and may not be well mixed in the population. These issues reduce the usefulness of profile databases drawn from a broad population: larger populations can have a lower profile relative frequency because of lower relatedness with the alleged contributor. Many evaluation methods do not adequately take account of distant relatedness, but its effects have become more pronounced with the latest generation of high-mutation-rate Y profiles.
Genes 2021, 12(8), 1209; DOI: 10.3390/genes12081209
Go to the paperLast updated: Aug 6, 2020.
Welcome to a series of 5 talks introducing a better way to report to a court the significance of matching Y-chromosome profiles between an evidence sample and its alleged source. The presenters are David Balding (University of Melbourne, Australia) and Mikkel M. Andersen (Aalborg University, Denmark).
Our new method complements previous approaches, for example based on computing a match probability: the new method becomes increasingly advantageous as Y-profiles become more informative (more loci, higher mutation rates).
Talk 1 presents the basic method and we recommend it be viewed first, the other four talks can then be viewed in any order. The series is intended for forensic scientists and others in the criminal justice system who encounter DNA evidence. Little scientific background is required for these talks, technical details are in scientific publications.
Note that all videos are available at our YouTube channel Y-talks 2020 by M. M. Andersen and D. Balding.
We invite you to use the Discussion feature of YouTube (available at each talk). You are also welcome to send us an e-mail (mikl{a}math.aau.dk / dbalding{a}unimelb.edu.au).
We would like to thank Andrew McDonald (Cellmark Forensic Services, currently at PathWest) for encouragement, feedback and help with dissemination.
1. A new approach to Y profile evaluation
Key reference: Andersen MM, Balding D (2017). How convincing is a matching Y-chromosome profile? PLoS Genetics, 3(11): e1007028, DOI: 10.1371/journal.pgen.1007028
2. Introduction to the malan (MAle Lineage ANalysis) R package.
Key reference: Andersen MM (2018). malan: MAle Lineage ANalysis. Journal of Open Source Software, 3(25), 684, DOI: 10.21105/joss.00684
3. Y-profile mixtures and profiled relatives.
Key reference: Andersen MM, Balding D (2019). Y-profile evidence: close paternal relatives and mixtures. Forensic Science International: Genetics, 38: 48-53, DOI: 10.1016/j.fsigen.2018.10.004
4. Using the Discrete Laplace method to compute a Y-profile match probability.
Note (Jun 29, 2022): The disclapmix R-package from version 1.7.4 has the function disclapmix_adaptive that makes estimation easier for the user.
Key reference: Andersen MM, Eriksen PS, Morling N (2013). The discrete Laplace exponential family and estimation of Y-STR haplotype frequencies. Journal of Theoretical Biology, 329: 39-51, DOI: 10.1016/j.jtbi.2013.03.009
5. The number of matches for a mitochondrial genome.
Key reference: Andersen MM, Balding D (2018). How many individuals share a mitochondrial genome? PLoS Genetics, 14(11): e1007774, DOI: 10.1371/journal.pgen.1007774