47,XYY Syndrome, also known as Jacob’s Syndrome, XYY Karyotype, XYY Syndrome or YY Syndrome is characterized in males by having two Y chromosomes, XYY, in contrast to the ‘normal’ XY set found in most males. It’s a common belief that having this extra Y chromosome is prone to make one more violent.
TV shows such as CSI: Miami, Criminal Minds and Law and Order have all aired one or more episodes in which a killer’s behavior is an outcome of an extra Y chromosome. These popular television shows are thought be a large contributor to why many believe the extra Y chromosome to be dangerous.
Published population surveys were done by The American Psychologists Association. The APS divided males into four groups: newborn males, normal adult males, and adult males in institutions for the mentally ill, and criminal males. “The frequency of XYY males was .13% for newborn and normal adult males, .70% for mentally ill males, and 1.93% for criminal males. Although XYY males are only a small proportion of perpetrators of violent crimes, their significantly higher frequency in the criminal population provides strong presumptive evidence for the association of an extra Y chromosome with aggressive behavior. Since Y chromosome is the male determining chromosome, the XYY genotype may be seen as highlighting the association between maleness and aggressive tendencies (psycnet).”
But according to genomiceducation, one large problem with these studies was ascertainment bias; if you look for something, it is often there. Because these men were already judged to be ‘abnormal’ by society, finding XYY chromosomes seemed like an easy explanation for behavior difficulties. But sometimes things are just a coincidence (genomicseducation).
In reality, there is no evidence that XYY leads directly to criminal behavior or violence. That is good news because approximately 1 in 1000 men are born with an extra Y chromosome.
I agree! Its TV shows such as the ones mentioned above that really make this believable to people. So many studies were done on this as well where the Texas sharpshooter problem was observed. More studies had people going to mental hospitals and jails to observe if there was an extra Y chromosome in men rather than surveying random people. Most studies did show a slight correlation between criminal or violent behavior and an extra Y chromosome however its been concluded that the conclusion YYX Syndrome does not make one more likely to be a criminal.
I had never hear about the possible correlation between an extra Y chromosome and violent men. I think that this is a hard hypothesis to prove because scientist have to consider the Texas sharpshooter problem. When observing people there are a number of other reasons that can explain a violent behavior, that has nothing to do with an extra Y chromosome. I encourage you to take a look at this link, which discuses a verity of reasons behind why people may be violent: http://www.psychologytoday.com/blog/stop-the-cycle/201112/why-do-people-resort-violence