LPI Topic 3 Flashcards
Heritability (h²)
- The proportion of variation in a trait within a population that is due to genetic differences.
- Does not measure how much of a trait is inherited by an individual.
Genotype vs. Phenotype
- Genotype: An individual’s genetic makeup.
- Phenotype: The observable characteristics resulting from both genes and environment.
Shared vs. Non-Shared Environment
- Shared Environment: Factors that siblings share (e.g., home, parents’ socioeconomic status).
- Non-Shared Environment: Unique experiences that differentiate individuals (e.g., friendships, personal experiences).
Twin Studies
- Compare monozygotic (MZ, identical) twins, who share 100% of their genes, with dizygotic (DZ, non-identical) twins, who share 50% of their genes.
- Greater similarity in MZ twins suggests genetic influence.
Adoption Studies
Compare adopted children with their biological and adoptive families to separate genetic and environmental influences.
Family Studies
- Examine trait similarities across generations to assess heritability.
- Cannot separate genetics from shared environmental effects.
Wilson Effect
- The heritability of intelligence increases with age (from ~20% in childhood to ~80% in adulthood).
- Reason: Genetic influences become stronger as individuals shape their environments.
Heritability Formula
- h²: Heritability estimate
- rMZ: Correlation between monozygotic twins
- rDZ: Correlation between dizygotic twins
Narrow vs. Broad Heritability
- Narrow Heritability: Focuses only on additive genetic variance (genes passed from parents).
- Broad Heritability: Includes additive, dominant, and epistatic genetic effects.
Assortative Mating
- Non-random mating where individuals choose partners with similar traits.
- Effect: Increases genetic similarity, inflating heritability estimates.
Gene-Environment Interactions
- Passive: Parents provide both genes and an environment that supports the trait (e.g., musical parents raise a child in a musical household).
- Evocative: A child’s genetic traits elicit specific responses from the environment (e.g., a sociable child attracts more friends).
- Active (Niche-Picking): Individuals seek out environments that match their genetic predispositions (e.g., intelligent individuals pursue academic activities).
Personality Traits Heritability
- Moderate heritability (~40-60%) based on twin studies.
- Traits such as openness and neuroticism show higher genetic influence.
- Environmental factors (particularly non-shared environment) significantly impact personality.
Intelligence Heritability
- Increases with age due to genetic-environment interaction (Wilson Effect).
- Estimated at 20-30% in childhood and 60-80% in adulthood.
Five Key Genetic Findings for Intelligence (Plomin & Deary, 2015)
- Heritability increases with age (Wilson Effect).
- Intelligence captures genetic effects across multiple cognitive abilities.
- Assortative mating for intelligence is higher than for personality.
- Intelligence is normally distributed (unlike psychiatric disorders).
- Intelligence is linked to social class and education, affecting life outcomes.
Genetic Variance is Not Simply Additive
- Genes do not contribute to traits in a simple way.
- Dominance & Epistasis (gene interactions) complicate heritability estimates.
Genes Change the Environment
Genetic influences can modify the environment individuals experience (e.g., a child genetically inclined to curiosity is more likely to seek out learning experiences).
Issues in Twin and Adoption Studies
- Equal Environment Assumption: Assumes MZ and DZ twins have similar environments, but MZ twins may be treated more similarly.
- Selective Placement in Adoption: Agencies may place children in environments similar to their biological backgrounds, confounding results.
Non-Random Mating (Assortative Mating)
Parents with similar genes have children, inflating heritability estimates in twin studies.
Heritability is Not Fixed
- Changes over time (e.g., intelligence becomes more heritable as people select environments that align with their genetic potential).
- Varies across different populations and historical periods.
Genetic Testing & Ethics
- Direct-to-consumer genetic testing (e.g., 23andMe) can reveal behavioural predispositions.
- Raises concerns about privacy, discrimination, and misuse of genetic data.
Misuse of Heritability Research
- Risk of genetic determinism (the false belief that genes entirely dictate behaviour).
- Potential social and political misuse (e.g., eugenics).
Intelligence, Social Mobility & Health
- Intelligence correlates with education, social class, and health outcomes.
- Raises ethical concerns about genetic screening and inequality.
