Asymmetries, heterosis, and phenotypic profiles of red junglefowl, White Plymouth Rocks, and F and F reciprocal crosses.

During the domestication of farm animals, humans have manipulated genetic variation for growth and reproduction through artificial selection. Here, data are presented for growth, reproductive, and behavior traits for the red junglefowl, a line of White Plymouth Rock chickens, and their F and F reciprocal crosses. Intra- and intergenerational comparisons for growth related traits reflected considerable additive genetic variation. In contrast, those traits associated with reproduction exhibited heterosis. The role of sexual selection was seen in the evolution of prominent secondary sexual ornaments that lend to female choice and male-male competition. The large differences between parental lines in fearfulness to humans were only mitigated slightly in the intercross generations. Whereas, overall F generation heterosis was not transferred to the F, there was developmental stability in the F, as measured by relative asymmetry of bilateral traits. Through multigenerational analyses between the red junglefowl and the domestic White Plymouth Rocks, we observed plasticity and considerable residual genetic variation. These factors likely facilitated the adaptability of the chicken to a broad range of husbandry practices throughout the world.