DNA Identification for Scientists: Basics
Biology and Information
The starting material for biological evidence is the DNA molecule that encodes for human life. A forensic identification is made when an evidence genotype matches a suspect genotype. But this identification must be tempered by the possibility of a coincidental match. This lecture introduces the likelihood ratio (LR) that balances DNA identification with coincidence.
Bayesian Belief Update
When there is uncertainty, our beliefs are expressed as probabilities. In science, we turn to data as a way of increasing our certainty in some hypotheses over others. Bayes theorem is the mathematical way we update our beliefs by examining data. This lecture visualizes Bayesian update, using coin tossing and medical diagnosis as examples.
Inclusion Genotype and LR
DNA identification science applies Bayesian update in two stages. First, examining genetic data updates our belief about the evidence genotype. Then, comparing this evidence genotype with specific and random suspects updates our LR belief in whose DNA contributed to the evidence. This lecture illustrates such reasoning using a simple interpretation of DNA mixtures.