Jacob’s XYY Theory

• Suggests some crime might be attributable to a chromosomal abnormality.

  46 chromosomes - 44 determine the shape and constitution of our body and only 2 determine sex.
• Sex is determined by the pattern of a person’s sex chromosomes.

  XX = woman.

  XY = man.

  It is the Y that makes a person male.
• A chromosome abnormality can include an extra chromosome.

  This is seen in the XYY condition.

  They have an extra Y chromosome.
• XYY men are sometimes called super males.

  They have been an interest to criminologists as they are more aggressive and more inclined to be violent than males with a single Y chromosome.
• Jacob suggested that men with the XYY syndrome were more aggressive than normal XY men.

  There are also some studies that suggest that XYY men are over-represented in the prison population. There are 15 sufferers per 1,000 in prisons and one per 1,000 in the general population.
• The serial killer John Wayne Gacy is said to have XYY syndrome.

  He sexually assaulted, tortured and killed at least 33 men in the USA.