This document discusses research into whether chromosomal abnormalities like XYY could be linked to criminal behavior. It summarizes a 1984 study by Alice Theilgaard that took blood samples from over 30,000 men to check for XXY and XYY patterns. Men with these patterns were interviewed and given intelligence and personality tests to see if they displayed more aggression. While XYY men tended to be slightly less intelligent and more aggressive, the sample sizes were small and a link between the abnormalities and criminality was not definitively proven. The study had limitations and left open ethical dilemmas about how such information could be used if a genetic link was established.