‘DNA: identity, relationships, and databases’ looks at the biological basis of DNA profiling and how DNA is analysed and interpreted in different case types. DNA evidence is useful because it combines empirical, real-world data with robust statistical analysis. Even a tiny sample of DNA evidence can give useful results, as it can be amplified using the polymerase chain reaction. The significance of the presence or absence of a DNA sequence can be measured using population genetics and statistics. As many criminals reoffend, most Western countries now compile DNA databases in order to help identify offenders, and to quickly eliminate large numbers of innocent individuals.