XYY syndrome is a chromosome disorder that affects males. Males with this disorder have an extra Y chromosome.

The XYY syndrome was previously considered the "supermale" syndrome where men with this condition were thought to be overly aggressive and more likely to become a criminal. These original stereotypes came about because several researchers in the 1960s found a high number of men with XYY syndrome in prisons and mental institutes. Based on these observations, men with XYY syndrome were labeled as overly aggressive and likely to be criminals.

These original observations did not consider that the majority of males with XYY syndrome were not in prisons or mental institutes. Since then, broader, less biased studies have been done on males with XYY syndrome. Though males with XYY syndrome may be taller than average and have an increased risk for learning difficulties, especially in reading and speech...