AO3 Twin Studies

Twin studies are used to investigate the ________ ________ of behaviour.

Twin studies are like an experiment. Match the concepts

• Extraneous variable

• Level of environmental similarity between MZ and DZ twins

• Independent variable

• Level of genetic similarity between MZ and DZ twins

• Dependent variable

• Concordance rates

If a twin study finds that a behaviour does have a genetic basis, then this means...

• The environment contributes to phenotype

• Phenotype contributes to genotype

• Genotype contributes to phenotype

• Phenotype contributes to the environment

The assumption underlying twin studies is that a set of MZ and DZ twins will have a ​ (a)   level of genetic similarity (100% similar for (b)   and 50% for (c)   ) but will have a (d)   level of environmental similarity (i.e., a set of MZ twins will grow up in just as (e)   an environment to each other as would a pair of DZ twins (e.g., each pair will grow up in the same house, with the same parents, and the same cultural experiences).

• MZ
• DZ
• Similar
• Different

P – A problem with the biological approach is its reliance on twin studies to investigate the genetic basis of behaviour.   

E – Twin studies assume that MZ twins share 100% of their genes, while DZ twins share 50%, but both experience equally similar environments (e.g., same home, parents, and culture). 

E – But critics argue that MZ twins' genetic similarity may lead to a more similar environment, as their identical appearance likely results in similar treatment. This introduces ​ (a)   variable in twin studies, making it unclear whether higher concordance rates stem from genetics, environment, or both. As a result, the ​ (b)   validity of twin studies in assessing genetic influences on behaviour is undermined.

• a confounding
• an independent 
• a dependent
• internal
• ecological
• external
• population

There are rare cases where DZ twins look identical. However, these “pseudo MZ twins” (meaning they look like MZ twins but aren’t actually MZ) do not tend to have higher concordance rates than typical DZ twins.

• This suggests twin studies do not have internal validity

• This suggests twin studies have internal validity