Related pairs will have values that, on average, correspond to the fixed values in traditional behavioral genetic models (e.g., siblings will have an average of .5), but including family members can artificially inflate heritability estimates because the shared environment is subsumed in the family coefficient. Therefore, eliminating pairs with Ajk estimates greater than .025 is recommended. Total phenotypic variance can then be decomposed into genetic and environmental components; because this method relies on unrelated individuals, there is no shared environmental variance component. Importantly, this same equation can be extended to include an additional variance estimate (Age) that indicates the extent to which the genetic variance is consistent across measured environments. Departure from this assumption provides evidence of gene-environment interaction without focusing on individual SNPs.
