Rose comb: an example of operational over-dominance in the domestic fowl

Abstract
The pleiotropic effect of the rose-comb gene (R) on fertility when combined with artificial selection against the single-comb type (r) results in an interesting example of operational over-dominance. An evaluation of the equilibrium frequency of the rose-comb gene based on this over-dominance concept provides a plausible explanation for the relatively high frequency of single-comb birds appearing in the Wyandotte breed of fowls.