 "k"+ carrier females are always of the fast normal-feathering type, while heterozygous "Kk"+ males are of the delayed-feathering type because of the dominance of "K" over "k"+.This regularity found practical use in commercial poultry breeding to separate chicks of different sexes in the hatcheries, thus avoiding the inconveniences associated with vent sexing and making easier, faster, harmless and cheaper the sex identification in one-day-old chicks.Through controlled matings and selection, "K" gene was put into egg-type breeds like White Leghorn, where sex-linked delayed feathering did not originally occur, thus obtaining genetically delayed-feathering female parent breeders to be mated with fast normal-feathering male parent breeders in order to obtain sexable female chicks of the fast normal-feathering type.