GENETICS OF HUMAN-BODY SIZE AND SHAPE - COMPLEX SEGREGATION ANALYSIS

The genetic component in a mixed heritability model, including major g ene, multifactorial and sibling environment transmissible components, was studied for some 20 anthropometric traits in two ethnically differ ent samples. The first sample comprised 305 Mexican nuclear families, and the second comprised 83 Ashkenazi Jewish nuclear families living i n Israel. All variables, after adjustment for age and sex, were subjec ted to principal-components analysis (PCA) in each sample separately. The mixed model of inheritance as implemented in the computer program POINTER was used in the present study. An attempt was made to evaluate genetic effects in the variation of the first principal components (P Cs). PCA showed a clear separation of variables and was easily interpr etable. The PC1 was a credibly general size factor. This factor alone accounted for about 30% of the total variance. Other components are ra ther shape factors for various combinations of traits. The testing of several genetic hypotheses showed the following: (1) For all fatter sc ores the genetic component was high and statistically significant. (2) In a Mexican sample, for PC1 and PC2, both major gene and polygenes c ontributed significantly to the total variation of these variables; in the major locus the alleles were most probably codominant. (3) For al l other PCs the major gene effect hypothesis was rejected, with more t han 50% of the variation attributable to the polygenes contribution. ( 4) No evidence was found for sibling environmental resemblance in eith er sample.