Final answer:
Broad-sense heritability considers all genetic contributions to phenotypic variance including interactions, while narrow-sense focuses on additive genetic variance alone. The difference is crucial in understanding the genetic basis of complex traits like personality, as seen in twin studies.
Step-by-step explanation:
Broad-sense heritability (H2) is the proportion of the phenotypic variance in a population that is attributable to the overall genetic variance, which includes additive, dominance, and epistatic variances. In contrast, narrow-sense heritability (h2) exclusively considers the additive portion of genetic variance, the effect of individual alleles without interactions. The former provides a wider scope of genetic influence including interactions between alleles, while the latter focuses on the genetic contribution to phenotypic variance that can be passed down from parents to offspring.
In the context of the Minnesota Study of Twins Reared Apart, high broad-sense heritability values for personality traits indicate a substantial genetic component. However, it does not discriminate between the types of genetic variance. Narrow-sense heritability would specifically dissect the additive genetic factors passed across generations that influence these personality traits. Understanding both heritability measurements provides insight into the heritability of complex traits like personality, factoring in not only direct genetic transmission but also the complexity of genetic interactions and environmental influences in shaping individual differences.