Genetic variance of weight and length in infant twins.

A population-based cohort of 166 twin pairs (67 monozygotic and 99 dizygotic) born at the Jackson Memorial Hospital/University of Miami Medical Center, from July 1, 1976 to December 31, 1980 was identified. Body weight and length were measured at 14 days and at one, three, six, nine, and 12 months of age. Statistically significant genetic variance was found for both body weight and length at each data point. Heritability for body weight increased from 0.28 at 14 days to 0.64 at one year. Corresponding values for body length were 0.16 and 0.48.