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The objectives of this research were to evaluate gender differences and selection on body weight as they affect growth curves of chickens. Marginal posterior densities of growth curve parameters were studied by Gibbs sampling on 10,671 male and female chickens originating from five lines. Line X−+ was selected on low body weight at 8 wk (BW8) and high body weight at 36 wk (BW36), line X+− on high BW8 and low BW36, X++ on high BW8 and BW36, X−− on low BW8, and BW36, and X00 was an unselected control line. Growth was modeled by a Gompertz function. Heritabilities and genetic correlations among parameters of the Gompertz curve were estimated. Marginal posterior densities were drawn for parameters of the growth curve and for sexual dimorphism at ages ranging from hatching to 1 yr. Lines selected for a higher BW8 had higher initial specific growth rates (L), higher maturation rates (K), and …