Which measure describes the frequency with which both members of twin pairs share a trait?

Which measure describes the frequency with which both members of twin pairs share a trait?

• A. Mutation rates
• B. Heritability
• C. Penetrance
• D. Concordance rates

Answer: (D)

Concordance rates describe how often both twins in a pair display the same trait. In twin studies, this is the probability that one twin is affected given that the other twin is affected, usually reported as a percentage. A higher concordance in identical (monozygotic) twins than in fraternal (dizygotic) twins suggests a genetic influence, while similar rates point to environmental factors. This measure is not about how often new mutations arise (mutation rates), nor is it about the overall genetic contribution to variation in a population (heritability), nor about the proportion of individuals with a genotype who express the trait (penetrance). For example, if the trait is concordant in a larger share of identical twin pairs than in fraternal pairs, that supports a genetic link for that trait.

Concordance rates describe how often both twins in a pair display the same trait. In twin studies, this is the probability that one twin is affected given that the other twin is affected, usually reported as a percentage. A higher concordance in identical (monozygotic) twins than in fraternal (dizygotic) twins suggests a genetic influence, while similar rates point to environmental factors. This measure is not about how often new mutations arise (mutation rates), nor is it about the overall genetic contribution to variation in a population (heritability), nor about the proportion of individuals with a genotype who express the trait (penetrance). For example, if the trait is concordant in a larger share of identical twin pairs than in fraternal pairs, that supports a genetic link for that trait.