What kind of heritability estimates (broad sense or narrow sense) are obtained from human twin studies?

Verified step by step guidance

1. Understand the difference between broad-sense heritability (H\^2) and narrow-sense heritability (h\^2). Broad-sense heritability includes all genetic variance (additive, dominance, and epistatic), while narrow-sense heritability includes only additive genetic variance.
2. Recognize that human twin studies typically compare trait similarities between monozygotic (identical) twins and dizygotic (fraternal) twins to estimate genetic influence on traits.
3. Note that because twin studies capture the total genetic contribution to trait variance (including additive and non-additive effects), the heritability estimates from these studies reflect broad-sense heritability rather than just narrow-sense heritability.
4. Recall that narrow-sense heritability is more specifically estimated using methods that focus on additive genetic variance, such as parent-offspring regression or SNP-based methods, which are not the primary focus of classic twin studies.
5. Conclude that heritability estimates from human twin studies are generally considered broad-sense heritability because they encompass all genetic variance components influencing the trait.

Key Concepts

Broad Sense Heritability (H²)

Broad sense heritability measures the proportion of total phenotypic variance in a population that is due to all genetic factors, including additive, dominance, and epistatic interactions. It reflects the overall genetic contribution to trait variation but does not distinguish between different genetic effects.

Narrow Sense Heritability (h²)

Narrow sense heritability estimates the proportion of phenotypic variance attributable specifically to additive genetic variance. This measure is important for predicting the response to selection because additive effects are transmitted from parents to offspring.

Human Twin Studies and Heritability Estimation

Human twin studies compare trait similarities between monozygotic and dizygotic twins to estimate genetic influence. These studies typically provide estimates closer to broad sense heritability because they capture all genetic effects shared by twins, not just additive genetic variance.