XYY and twin/adoption studies

• people with the XYY chromosome are known as...

  super-males
• out of 1000 men in prison, how many men had the XYY chromosome and how many men out of 1000 in the general public had the XYY chromosome?

  15= prison

  1= general public
• who allegedly had the XYY chromosome and what did he do?

  John Wayne Gacy and he sexually assaulted, tortured and murdered at least 33 men in the USA.
• who found some links between the syndrome and property crime?

  Price and Whatmore
• why can XYY males be over-represented?

  because they often have low intelligence, meaning they are more likely to be caught.
• twin theories: why does crime often run in the family?

  blood relatives share many of the same genes- therefore if one person in the family has criminal genes, someone else in the family may also have these genes.
• what is the difference between dizygotic twins and monozygotic twins?

  DZ= two separate eggs and share 50% of the DNA.

  MZ= one egg and share 100% of the DNA.

  both born at the same time.
• what is the concordance rate?


  the probability (as a percentage) that if one twin has a characteristic the other twin will also have the characteristic.
• Johanne Lange (1929) investigated 13 MZ twins and 17 DZ twins, what were the findings?


  - found that 10 of the 13 MZ twins had both served time in prison

  - only 2 of the 17 DZ twins had both served time in prison.
• Christiansen (1977) investigated 3586 twin pairs born in the eastern half of Denmark and found what?

  - MZ twins are more likely to become criminals if one twin is a criminal. (35%)

  - also showed that males are more likely to be a criminal than females.
• adoption studies: Hutchings and Mednick (1975) studied 14,000 adopted children and found a high proportion of what?


  boys with criminal convictions had biological parents with criminal convictions too.
• what does Hutchings and Mednick research suggest?

  suggests that there is a strong link between genetics and criminality.
• what did the study find about criminality between the adopted parents and adopted offspring?

  that there was no relationship between the number of criminal convictions adopted parents had and their adopted offspring.
• what did Gottfredson and Hirschi say about adoption studies?

  they argue that genes have little effect on criminality because often, adopted children are placed in similar environments to those of their birth family. similar environment= similar behaviour