How are heritability measures reached?
There are two main types of study. One type involves studies which compare children within the same family, who are normally genetically related, with other children. By itself, however, such a study will not discriminate between the effects of the shared genes of the siblings and those of their shared family environment. So such studies are sometimes enriched by comparing the similarities between genetic siblings with those between genetic and non-genetic siblings (adopted and step children) in the same family, in the belief that differences here will show the differential effects of different genes in a shared environment. But considerable caution needs to be exercised in assuming that the environment is shared: within a single family different children will have different relationships with their siblings and parents, and these environmental differences will often be exacerbated where adopted and step children are involved. So there is plenty of scope for gene-environment interactio
