Probabilistic genotyping in forensic DNA analysis

Since forensic DNA probabilistic genotyping (PG) software was introduced nearly a decade ago, its use by federal, state, and local forensic laboratories has increased substantially.

PG software makes better use of the information contained in a DNA profile than traditional approaches. As a result, DNA profiles once discarded as uninformative are now accessible for inculpating and exculpating potential donors of forensic biological evidence. Users of PG software have been able to improve their ability to interpret low-level, degraded, and mixture DNA profiles, positively impacting interpretation of DNA results from a wide range of evidence.

Benefits of Enhancing Interpretation of DNA Evidence

The advent of PG software has enabled forensic analysts to interpret more challenging DNA profiles with greater efficacy and at a much higher degree of accuracy than any interpretational approach previously used.

PG software has proven particularly effective in producing usable, interpretable, and valid DNA results in criminal cases, and excluding individuals wrongly associated as the source of crime scene evidence. PG tools have also been instrumental in helping to solve cold cases in which evidence originally dismissed as inconclusive could be reanalyzed, helping to develop investigative leads and support exonerations in post-conviction cases.

Employing methods like Markov Chain Monte Carlo that are routinely used in computational biology, physics, engineering, weather prediction, and the stock market, PG software grades proposed profiles on how closely they resemble or can explain an observed DNA mixture profile. From there, the probability of the observed DNA evidence can be calculated under two propositions – if the DNA originated from a person of interest or if the DNA originated from an unknown donor. These two probabilities are then presented as a likelihood ratio.

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