In birds, males are homogametic sex (XX), females are heterogametic (XY). Light Sussex fowls have mostly white plumage (feathers), and Rhode Island fowls have mostly red. The character white-feathered (R) is dominant to the character red (). 2.1 Explain why, on mating Rhode Island cockereis with white Sussex hens, all male offspring have white plumage and all females red. [18]​