behavioural genetics
Summary
Behavioral genetics studies how genetic and environmental differences among people contribute to differences in behavior and traits, using twin, adoption and family studies. Most testable: heritability describes variation within a population, not how much of one person's trait comes from genes.
Detail
Meaning: Behavioral genetics asks how much of the variation in a trait, such as intelligence, personality or risk of a disorder, is linked to genetic differences and how much to environmental differences. Most traits are polygenic and show gene–environment interaction, so genes set tendencies rather than fixed outcomes.
Equation: h² = VG / VP, where h² is heritability (a unitless fraction from 0 to 1), VG is the variance in the trait due to genetic differences, and VP is the total phenotypic variance in the population (both in squared units of the trait).
On the MCAT: Passages describe twin or adoption studies. Monozygotic twins share nearly all their genes, while dizygotic twins share about half of the genes that differ between people, like ordinary siblings. If monozygotic pairs are more alike (higher concordance) than dizygotic pairs, a genetic influence is suggested. Monozygotic twins raised apart who stay similar also point to genes. An adopted child resembling biological parents suggests genes, while resembling adoptive parents suggests shared environment. Concordance well below 100% in monozygotic twins points to environmental influence.
Common confusion: Heritability applies to a population, not an individual. A heritability of 0.6 does not mean 60% of your own trait is genetic. It is also not fixed, because it depends on the population and environments studied. High heritability does not mean a trait cannot be changed: height is highly heritable, yet nutrition can still change it.
Sources
- Psychology (Myers)
- Psychology (Schacter, Gilbert, Wegner)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.