Visiting Student Seminar – Maria Simonsen. Wednesday, 27 April 2016 10:30 AM-11:30 AM

Title:   Using the Multi-Allelic Wright-Fisher Model to Investigate the Validity of Current Forensic DNA Match Probabilities and to Propose Alternatives

When: Wednesday, 27 April 2016 10:30 AM-11:30 AM

Where: GP-Y Block, Level 8, Room 801


  • Maria Simonsen is a PhD Student at Bioinformatics, Aarhus University, Denmark.
  • Her Phd project: Population genetic models for allele frequencies aims to develop mathematical models for genetic variation and make statistical inference based on the analytical expression of the behaviour of the mean and the (co)variance structure of allele frequencies over time.
  • Maria has been collaborating with Professor David Balding at the University of Melbourne for the last three months.


In forensic DNA profiling the match probability measures the weight of evidence for an individual to be the contributor of interest to a crime-scene DNA sample. For more than 20 years the Balding-Nichols match probability formulas have been widely used. These are based on assuming that the alleles in the genotypes of the alleged and alternative contributors are sampled from a subpopulation in which the allele fractions follow the Dirichlet distribution. It has from the start been noted that the Dirichlet assumption is only approximate, because the short tandem repeat (STR) loci used in forensics evolve according to a single-step mutation (SSM) model, generating correlations among neighbouring alleles that cannot be accommodated under the Dirichlet. However the validity of the Balding-Nichols match probabilities has never been systematically investigated.  We now attempt this by simulating STR allele frequencies under a diffusion approximation to the Wright-Fisher with SSM model. We find that the Dirichlet model is often not sufficiently flexible to encapsulate key features of the simulated allele frequency distributions, and we suggests a more appropriate approximation and describe its implications for forensic match probabilities.

This is joint work with David Balding from Melbourne University and Asger Hobolth from Aarhus University.

Meeting with Maria:

Maria will also be on campus from midday Tuesday 26th April.  If you would like to meet her please contact Daniel Kennedy to arrange a time



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