Quantitative and Molecular Genetics of a Three - Generation Intercross Between Chickens Selected for Low Body Weight and Red Junglefowl

The process of domestication of the chicken had knowingly and unknowingly employed genetics to achieve human perceived changes in economic traits such as growth and egg production. These changes sometimes resulted in negative side effects, such as a physiological delay in sexual maturity observed in a line of White Plymouth Rock chickens selected for low body weight. These chickens plateaued after about 30 generations of selection possibly due to a conflict between survival/reproduction and the selection for slow growth. Yet, the even smaller red junglefowl seem to be free of such physiological barriers.

Here, data are presented for reproductive, growth, and behavioral traits for the Richardson strain of red junglefowl, a line of White Plymouth Rock chickens that has undergone 57 generations of selection for 8-week body weight and their F1 and F2 reciprocal crosses. While exploring the physical and genetic differences between domestic chickens, as well as the genetic basis for the striking differences in growth patterns between the two lines, observed was plasticity and considerable residual genetic variation which likely facilitated the adaptability of the chicken to a broad range of husbandry practices. Differences in growth patterns implied additive and non- additive genetic variation and modifications in resource allocation strategies during domestication.