Analysis of behavioral traits in the presence of cultural transmission and assortative mating: Applications to IQ and SES

General linear models of familial resemblance are described which allow for polygenic inheritance, cultural transmission from parent to offspring, phenotypic assortative mating, common environment, and maternal and parental effects. These models use observed phenotypic correlations between multiple classes of relatives and/or correlations between individuals reared in separated and extended family structures to yield maximum likelihood parameter estimates. The models are first applied to American kinship data for IQ, with the variance of IQ partitioned as 30% additive genetic, 29% due to cultural inheritance, 9% due to gene-culture covariance, and 32% due to nontransmissible environment. Under the assumption that the correlations between (nontransmissible) environments of DZ and MZ twins are the same, an approximate treatment of dominance yields an estimate of 23% dominance variation.