Genetic Similarity ERQ

Genetic similarity

The degree to which individuals share the same genetic material, such as monozygotic twins (100%) or dizygotic twins (50%).

Twin studies

By comparing concordance rates in MZ and DZ twins, researchers estimate how much behaviour is influenced by genes versus environment.

Heritability

A statistical estimate of the proportion of behavioural variation in a population that is due to genetic differences.

Aim of McGue et al. (2000)

To investigate genetic and environmental influences on adolescent tobacco and marijuana use.

Method of McGue et al. (2000)

Correlational twin study comparing MZ and DZ twins using interviews and questionnaires on drug use and family environment.

Key findings of McGue et al.

Tobacco use showed moderate heritability (40-60%), marijuana use showed low heritability (10-25%), with strong environmental influences.

Conclusion of McGue et al.

Both genes and environment affect behaviour, but environmental influences like family norms have a greater effect on drug use.

Strengths of McGue et al.

Large sample, clear twin design, practical insights for drug prevention, balanced view of genes and environment.

Limitations of McGue et al.

Self-report bias, correlational design, focus limited to two drugs, cultural/time-specific context.

Aim of Kendler et al. (2006)

To investigate the heritability of Major Depressive Disorder (MDD) and explore sex differences in heritability.

Participants in Kendler et al. (2006)

15,493 complete twin pairs (MZ and DZ) from the Swedish national twin registry, including both male and female twins.

Method used in Kendler et al. (2006)

Large-scale twin study using telephone interviews conducted over 4 years; diagnosis based on DSM-IV criteria and antidepressant prescriptions.

Procedure of Kendler et al. (2006)

Twins were interviewed about depressive symptoms and medication history. Concordance rates were calculated and compared for MZ and DZ twins. Time spent living together was also analyzed.

Main results of Kendler et al. (2006)

Average heritability of MDD was 38%. MZ twins had higher concordance than DZ twins. Female MZ: 44%, Female DZ: 16%, Male MZ: 31%, Male DZ: 11%.

Conclusion of Kendler et al.

MDD is influenced by genetics, with higher heritability in women. Environmental factors also contribute, and sex-specific genetic risks may exist.

Strengths of Kendler et al.

Very large, representative sample; reliable diagnostic criteria; shows genetic influence with sex-based nuance; ruled out shared environment effects.

Limitations of Kendler et al.

Doesn't identify specific genes; cannot establish cause-effect; only measures concordance without biological mechanisms.

Support for genetic similarity in behaviour

Both studies show that greater genetic similarity (MZ twins) leads to higher concordance in behaviours like drug use and depression, suggesting genetic influence.

Extent of genetic similarity's effect on behaviour

It plays a significant role, but not in isolation. Environmental context and individual experiences shape how genetic predispositions manifest.

Conclusion of the ERQ

Genetic similarity influences behaviours like addiction and depression, but behaviour is shaped by gene-environment interaction and varies by context and individual differences.