Discuss the extent to which genetics influences behavior
Attempt to determine the effect of a particular gene on behavior such as psychological traits (temperament), psychological disorders (e.g. depression or schizophrenia) or various physiological conditions.
Study to use: Caspi et al. (2003)
- Monozygotic twins (MZ or identical twins) come from the same egg and share 100% of their genes. Dizygotic twins (DZ or fraternal twins) come from two different eggs and share around 50% of their genes. Siblings share 50% of their genes.
- The researchers calculate concordance rate (the likelihood or probability that if one individual has the trait the other will also have it). The concordance rate is assumed to establish if or to what extent a certain trait is inherited.
- In twin studies, one twin acts as control for the other twin. The classic twin study only studied concordance rates and did not include environmental factors. In some cases MZ twins were raised apart and in these cases it was assumed that differences were due to environmental factors.
- In twin research, sets of MZ are compared with sets of DZ twins for a particular trait or disorder. High concordance rates in MZ twins and lower concordance rates in DZ twins for the same behavior indicate that the trait or disease is linked to genes (inherited). Differences within pairs of identical twins are attributed to environmental factors.
Study to use: Bouchard et al. (1990)