Twin & adoptive studies

• Twin studies

  Twins compared on similar trait to see how similar they are

  If a particular behaviour is entirely genetic - expect MZ twins to show 100% concordance

  If behaviour more genetic than environmental - expect higher concordance in MZ than DZ twins
• Twin studies strength 1

  Can investigate gene influence because MZ and DZ twins share environment therefore only diff is genes
• Twin studies strength 2

  Info from twin registries - 1000s of twin data + info on many twin variables so large sample and representative data
• Twin studies weakness 1

  Broad indication of behaviour being genetic - not specific genes so require more recent tech
• Twin studies weakness 2

  Can overestimate genetic influence - MZ have more similar environment than DZ (treated more similarly, spend more time tg etc) so similarity is due to shared environment
• Adoptive studies

  Genetic factors implicated if children more similar to biological parents (share genes) than adoptive parents (share environment) & environmental factors implicated if converse
• Adoptive studies strength 1

  Removes EV of environment - either biology not shared or environment
• Adoptive studies strength 2

  Shows overestimation of genetic factors in twin studies
• Adoptive studies weakness 1

  Adoptive fams may be similar to biological ones (selective placement) - environmental influences similar
• Adoptive studies weakness 2

  Adoptive parents are unusual - unlikely representative of pop (better educated, financially well off etc)