🧠 Genetic Similarities and Twin Studies

📌Core Concepts

Twin and family studies are classic tools to separate genetic from environmental influences. Monozygotic (MZ) twins share ~100% of their DNA, while dizygotic (DZ) share ~50%, allowing comparison of heritability estimates.

📌Key Studies

Key Study 1: Kendler et al. (2006)

  • Aim: Investigate heritability of major depression.
  • Method: Over 42,000 Swedish twins studied via registry data.
  • Findings: Heritability of depression ≈ 38%; higher in women.
  • Conclusion: Genetic factors moderately contribute to depression, but environment remains key.
  • Evaluation:
    • 👍 Large, representative sample.
    • 👎 Correlational; cannot pinpoint causal genes.

Key Study 2: McGuffin et al. (1996)

  • Aim: Examine concordance rates for depression.
  • Findings: MZ = 46%; DZ = 20%.
  • Conclusion: Genetic factors strongly implicated; environment still important.

Key Study 3: Scarr & Weinberg (1983)

  • Adoption study on intelligence: adopted children resembled biological parents more in IQ → genetic influence significant.

🔍Tok link


How do probabilistic correlations challenge what it means to “know” something scientifically?

Can statistical data truly explain human individuality?

 🌐 Real-World Connection

  • Twin registries used in studying addiction, personality, and schizophrenia.
  • Policy implications for early screening and interventions.

❤️ CAS Link

  • Create informative posters explaining twin research ethics

🧠  IA Guidance

  • Model twin correlations through small class surveys comparing siblings’ traits.

🧠 Examiner Tips

  • Always explain why twin studies are used (control for genes).
  • Avoid stating “genes cause behaviour” — always refer to interaction.