🧠 Genetic Inheritance and Behaviour

📌Key terms

Term	Definition
Genotype	The genetic makeup of an individual.
Phenotype	Observable characteristics resulting from genotype-environment interaction.
Heritability	The proportion of observed variation in a trait that can be attributed to genetic factors.
Gene expression	The process by which information from a gene is used to synthesize functional products like proteins, influenced by environment.
Epigenetics	Study of how environmental factors affect gene expression without altering DNA sequence.

📌Core Concepts

Genetic inheritance refers to the transmission of biological traits from parents to offspring through genes. In psychology, it explores how inherited genetic information influences behaviour, personality, intelligence, and susceptibility to mental disorders.

Genes affect brain structure, neurotransmitter systems, and hormone regulation — which, in turn, influence cognition, emotion, and behaviour. However, behaviour is polygenic and shaped by complex gene–environment interactions(GxE).

📌Key Studies

Key Study 1: Bouchard and McGue (1981)
Meta-analysis of intelligence studies among twins and families.

• Aim: To investigate the heritability of intelligence.
• Method: Reviewed 111 twin studies comparing IQ correlations in MZ (identical) and DZ (fraternal) twins reared together/apart.
• Findings: MZ twins reared together = 0.86 IQ correlation; MZ apart = 0.72; DZ together = 0.60.
• Conclusion: Intelligence has a significant genetic component (~70%), but environment still plays a role.
• Evaluation:
  • 👍 Large sample increases reliability.
  • 👎 Publication bias possible; “intelligence” operationalization varies.
  • 👎 Correlational; cannot infer causation.

Key Study 2: Caspi et al. (2003)
Gene–environment interaction and depression.

• Aim: To test the influence of the 5-HTT gene (serotonin transporter) on depression.
• Method: Longitudinal study; 847 New Zealand adults genotyped for short (s) and long (l) alleles.
• Findings: Those with two short alleles had more depressive symptoms following stressful events.
• Conclusion: Genetic vulnerability interacts with environmental stress → supports diathesis–stress model.
• Evaluation:
  • 👍 Real-world applicability to mental health risk.
  • 👎 Self-report bias; correlational; ethics in genetic disclosure.