Heritability of Intelligence

Question 1

What is heritability?

Answer 1

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

Question 2

Is heritability a fixed measure?

Answer 2

No, heritability changes based on age, environment, and population context.

Question 3

Does heritability apply to individuals?

Answer 3

No, heritability is a population statistic and cannot explain individual differences.

Question 4

What is the genotype?

Answer 4

The internal genetic code that influences traits, such as cognitive abilities or personality.

Question 5

What is the phenotype?

Answer 5

The outward expression of the genotype, such as IQ score or observed personality traits.

Question 6

What is the difference between genotype and phenotype?

Answer 6

Genotype refers to internal genetic coding, while phenotype is the observable expression of that coding.

Question 7

How does heritability change with age?

Answer 7

Genetic influence strengthens over time as individuals self-select environments.

Question 8

What is the Wilson Effect?

Answer 8

The phenomenon where the heritability of IQ increases with age due to greater alignment between genetic predispositions and self-selected environments.

Question 9

What is the formula for calculating heritability in twin studies?

Answer 9

The formula involves the correlation coefficients for monozygotic and dizygotic twins.

Question 10

What do shared and non-shared environments mean?

Answer 10

Shared environments include influences common to family members, while non-shared environments consist of unique individual experiences.

Question 11

Can the same environment affect siblings differently?

Answer 11

Yes, for example, parental divorce might affect one sibling more than another, making it a non-shared environmental influence.

Question 12

What are the three types of gene-environment correlations?

Answer 12

1. Passive Effects: Genes align with the environment provided by parents.
2. Active Effects: Individuals select environments matching their genetic tendencies.
3. Evocative Effects: Genetic traits elicit specific responses from the environment.

Question 13

How is heritability of height influenced by the environment?

Answer 13

In stable environments with less variance, the heritability of height increases.

Question 14

What is narrow heritability?

Answer 14

The proportion of variance explained by additive genetic effects alone.

Question 15

What is broad heritability?

Answer 15

The proportion of variance explained by additive, dominant, and epistatic genetic effects combined.

Question 16

What is dominant genetic variance?

Answer 16

When one gene’s effect is stronger and overrides the other.

Question 17

What is epistatic genetic variance?

Answer 17

The interaction between genes, where their combined effect is greater than the sum of their individual effects.

Question 18

How do twin studies estimate heritability?

Answer 18

By comparing the similarity of monozygotic (MZ) twins, who share 100% of genes, and dizygotic (DZ) twins, who share 50%.

Question 19

What is a worked example of heritability in IQ?

Answer 19

If MZ twins have an 86% concordance rate and DZ twins have 55%, heritability can be calculated.

Question 20

How do adoption studies measure heritability?

Answer 20

By comparing traits in adopted children with biological parents (genetic influence) and adoptive parents (environmental influence).

Question 21

What are some limitations of twin studies?

Answer 21

1. MZ twins may experience more similar shared environments than DZ twins.
2. Twins often have low birth weights, making them less representative of the general population.

Question 22

What are some limitations of adoption studies?

Answer 22

1. Adoptive families are often socioeconomically homogenous.
2. Adopted children may not represent the general population due to selective adoption criteria.

Question 23

What is assortative mating?

Answer 23

The tendency to choose mates with similar traits, increasing genetic similarity in offspring.

Question 24

How does the heritability of intelligence vary by age?

Answer 24

In childhood, shared environment has a stronger influence; in adulthood, genetic influences become stronger.

Question 25

Why does heritability not tell us which genes contribute to a trait?

Answer 25

Heritability estimates reflect variance, not specific genetic contributions, and many traits are influenced by multiple genes with small effects.

Question 26

What residual effects might account for unexplained variance in heritability studies?

Answer 26

Non-shared environments, measurement errors, and other genetic or biological factors.

Question 27

How do dynamic changes in heritability complicate research?

Answer 27

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.

Question 28

Why might heritability findings from twin studies be biased?

Answer 28

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.