ESTIMATION OF ENVIRONMENTAL AND GENETIC COMPONENTS OF QUANTITATIVE TRAITS WITH APPLICATION TO SERUM-CHOLESTEROL LEVELS

Abstract

A mixed model of environmental, polygenic and major locus effects is developed, allowing for environmental correlations between 1st-degree relatives and spouses. Maximum-likelihood techniques are used to determine the relative contributions of each of these effects to a quantitative trait. Inclusion of a nuclear family in the sample is assumed to depend on the value of the quantitative trait of 1 member of the family, so conditional distributions are used. Application of the method to serum cholesterol data from the general population shows that the addition of a polygenic effect to a model that assumes only an environmental effect makes a significant improvement. A completely dominant single gene influences serum cholesterol levels. Cholesterol levels were adjusted for a range of factors, such as age, sex, weight/height2, and marital status, but environmental factors still account for about half the variability in the residual values.