Selected blood variables were studied in 165 French Canadian boys and girls aged 6–15 years from the Center for Research on Human Growth at the University of Montreal. Venous blood samples were obtained between 1968 and 1971, and results closest to 10 years of age are retained for the present analysis. A maximum of 124 pairs of sibs were studied for hemoglobin concentration, hematocrit, total cholesterol, concentration of carotene, vitamin A and serum iron, iron-binding capacity, and saturation of transferrin. Sibling correlations ranged from essentially zero (0.06; hematocrit) to 0.51 (carotene) with the effect of age controlled. An estimate of the contribution of nonbiological factors to covariation between sibs was attempted through statistical control of the following seven indicators: education of father and of mother, occupation of father and of mother, total family income, size of household, and dollars spent on food per capita per week. This procedure lowered correlations by a substantial amount, particularly serum iron concentration, iron-binding capacity, and percentage saturation of transferrin (about 0.20 correlations units). Only cholesterol (0.30) and carotene (0.42) maintained a moderate positive coefficient. Broad heritability estimates computed after such statistical controls of nonbiological familial effects ranged from zero to 0.84. Total genetic effects for cholesterol, in this normolipemic population, reached a fairly high value of 0.6
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