Heritability of Intelligence Flashcards
What is heritability?
The proportion of variance in a trait across a population that can be attributed to genetic differences.
OR: how much of a trait’s differences are caused by genetics
Is heritability a fixed measure?
No, heritability changes based on age, environment, and population context.
Does heritability apply to individuals?
No, heritability is a population statistic and cannot explain individual differences.
What is the genotype?
The internal genetic code that influences traits, such as cognitive abilities or personality.
What is the phenotype?
The outward expression of the genotype, such as IQ score or observed personality traits.
What is the difference between genotype and phenotype?
Genotype refers to internal genetic coding, while phenotype is the observable expression of that coding.
How does heritability change with age?
Genetic influence strengthens over time as individuals self-select environments.
What is the Wilson Effect?
The phenomenon where the heritability of IQ increases with age due to greater alignment between genetic predispositions and self-selected environments.
What is the formula for calculating heritability in twin studies?
The formula involves the correlation coefficients for monozygotic and dizygotic twins.
What do shared and non-shared environments mean?
Shared environments include influences common to family members, while non-shared environments consist of unique individual experiences.
Can the same environment affect siblings differently?
Yes, for example, parental divorce might affect one sibling more than another, making it a non-shared environmental influence.
What are the three types of gene-environment correlations?
- Passive Effects: Genes align with the environment provided by parents.
- Active Effects: Individuals select environments matching their genetic tendencies.
- Evocative Effects: Genetic traits elicit specific responses from the environment.
How is heritability of height influenced by the environment?
In stable environments with less variance, the heritability of height increases.
What is narrow heritability?
The proportion of variance explained by additive genetic effects alone.
What is broad heritability?
The proportion of variance explained by additive, dominant, and epistatic genetic effects combined.
What is dominant genetic variance?
When one gene’s effect is stronger and overrides the other.
What is epistatic genetic variance?
The interaction between genes, where their combined effect is greater than the sum of their individual effects.
How do twin studies estimate heritability?
By comparing the similarity of monozygotic (MZ) twins, who share 100% of genes, and dizygotic (DZ) twins, who share 50%.
What is a worked example of heritability in IQ?
If MZ twins have an 86% concordance rate and DZ twins have 55%, heritability can be calculated.
How do adoption studies measure heritability?
By comparing traits in adopted children with biological parents (genetic influence) and adoptive parents (environmental influence).
What are some limitations of twin studies?
- MZ twins may experience more similar shared environments than DZ twins.
- Twins often have low birth weights, making them less representative of the general population.
What are some limitations of adoption studies?
- Adoptive families are often socioeconomically homogenous.
- Adopted children may not represent the general population due to selective adoption criteria.
What is assortative mating?
The tendency to choose mates with similar traits, increasing genetic similarity in offspring.
How does the heritability of intelligence vary by age?
In childhood, shared environment has a stronger influence; in adulthood, genetic influences become stronger.
Why does heritability not tell us which genes contribute to a trait?
Heritability estimates reflect variance, not specific genetic contributions, and many traits are influenced by multiple genes with small effects.
What residual effects might account for unexplained variance in heritability studies?
Non-shared environments, measurement errors, and other genetic or biological factors.
How do dynamic changes in heritability complicate research?
Changes in environmental stability or age-related independence affect the relative contributions of genes and environment.
OR: Changes in stable environments or growing independence with age can change how much genes and environment each matter.
Why might heritability findings from twin studies be biased?
Identical twins often share more similar environments than fraternal twins, inflating heritability estimates.
OR: Identical twins usually have more similar environments than fraternal twins, which can make heritability estimates seem higher.
