My games typically have the red eye of American games but occasionally they throw offspring with dark eyes. Eye coloration does not appear to be linked to feather coloration. When I cross a red eyed game rooster (out of a dark eyed hen) with a red jungle fowl hen, three female offspring have dark brown eyes and while four brothers do not. At least one of pullets from same cross that is no longer had red eyes. Is eye coloration normally sex-linked on Z-chromosome?