Multifactorial Genetic Models for Quantitative Traits in Humans

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Abstract
Quantitative traits measured in human families can be analyzed to partition the total population variance into genetic and environmental components, or to elucidate the genetic mechanism involved. The estimation of variance components was reviewed directly from human pedigree data and was also reviewed in the form of path coefficients from correlations between pairs of relatives. To elucidate genetic mechanisms, a mixed model that allows for segregation at a major locus, a polygenic effect and a sibling environmental correlation was described for nuclear families. In each case appropriate likelihoods were derived as a basis, using numerical maximum likelihood methods, for parameter estimation and hypothesis testing. A general model was described that allowed for several familial sources of environmental variation, assortative mating and both major gene and polygenic effects; and an algorithm for calculating the likelihood of a pedigree under this model is indicated. Some of the remaining problems in this area of biometric analysis are pointed out.