An incompletely dominant gene controls the color of chickens so that BB produces black, Bb produces blue, and bb produces white. A second gene controls comb shape, with the dominant gene R producing a rose comb and r producing a single comb. If a chicken that is pure-breeding for both black color and rose comb is mated to a white chicken with a single comb, what fraction of the offspring in the F2 generation will be black with a rose comb