Twin studies

• What are monozygotic twins?

  Identical twins who have developed from the same fertlised egg and share 100% of their DNA.
• What are dizygotic twins?

  Non-identical twins who develop from different fertilised eggs and they share 50% of their DNA.
• What idea do twins studies support?

  That a heritable trait might increase the risk of criminal behaviour
• What was Lange's research 1929?

  10/13 monozygotic twins has both served time in prison, only 2/17 dizygotic twins had both served time in prison.
• What was the research conducted by Christiansen 1977?

  He studied 3,586 pairs of twins and found a concordance rate of 35% for monozygotic twins and 13% for dizygotic twins.
• What are the strengths/positives of twin & adoption studies?

  The results of twin studies have helped to prevent vulnerable disorders which means people can get helped before their condition gets worse. As adopted children are exposed to a different environment to their biological family, it is easier to seperate genetic and environmental factors.
• What are the limitations/weaknesses of twin & adoption studies?

  The small sample sizes involved in twin studies don't represent the general population and therefore we can't generalise the findings.

  In adoption studies, late adoption age means the children might have already been influenced by their birth parents and their foster parents so we can't determine the causes of their behaviour.

  A problem with twin studies is that the twins are often brought up in the same environment so their criminality could be because of their environment, not their genetics.