Studies of heritability in humans that assume that if genes influence a certain trait, close relatives should be more similar with that trait than distant relatives are called ________ studies.

A) strain
B) selection
C) family
D) twin

Family studies examine the extent to which genetic and environmental factors contribute to a certain trait by comparing the degree of similarity among relatives of various degrees of kinship. This is done by comparing the resemblance of first-degree relatives (parents, siblings, and offspring), who share 50% of their genes on average, to that of second-degree relatives (cousins, grandparents, aunts/uncles & nieces/nephews), who share 25% of their genes on average.