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A genetic basis to growth and development has been demonstrated in many heritability studies of anthropometries. Although such measures describe the extent of grow that particular times, they do not fully address the process of growth. We applied a three-parameter curve-fitting function to serial measures of recumbent length from 569 infants (birth to 2 years of age) in 188 families enrolled in the Fels Longitudinal Study. This yielded three growth pattern parameters that represented estimated recumbent length at birth (parameter 1), rate of growth (parameter 2), and intrinsic rate of change in growth (parameter 3). The growth pattern parameter estimates for each individual were examined in a series of genetic analyses using a maximum -likelihood method for pedigree data. Significant heritabilities were found for all three growth pattern parameters: parameter 1, h2 — 0.83 ± 0.12; parameter 2, h2 = 0.67 ± 0.18; and parameter 3, h2 = 0.78 ± 0.17. In addition, genotype by sex interaction was indicated for growth pattern parameters 2 and 3, suggesting that the genes influencing rate of growth and intrinsic rate of change in growth are them selves influenced by the sex of the individual.