a chromosomal anomaly found in 1961 and correlated to males who demonstrated aggressive or violent behavior in criminal facilities. It was initially presumed that the extra Y chromosome set males up for these actions, but the theory was changed as XYY anomalies were later discovered in normal males. Commonly referred to as double-Y condition.

XYY SYNDROME: "XYY syndrome is when a male has two Y chromosomes. "
Cite this page: N., Sam M.S., "XYY SYNDROME," in PsychologyDictionary.org, April 29, 2013, https://psychologydictionary.org/xyy-syndrome/ (accessed October 21, 2021).