Chromosomes of the sterile hybrid duck

The hybrid duck resulting from the mating of a Muscovy male and a White Pekin female is sterile. Utilizing a technique for the culture of blood cells, chromosome preparations were made of the parental and hybrid ducks. Morphological differences were found to exist between the first and fourth pairs of chromosomes of the Muscovy and the White Pekin. The first pair of chromosomes has a long-to-short arm ratio of 2:1 in the Muscovy and 1.6:1 in the White Pekin. The sex chromosome pattern of both species was found to be ZZ/ZW, rather than ZZ/ZO, with the Z and the W occupying relatively the same positions in the different ducks. The fourth pair of chromosomes, representing the sex chromosomes of the male duck, possesses short arms in the White Pekin but not in the Muscovy. This difference in morphology is probably significant with reference to the sterility of these hybrids. Studies of the gonads have indicated that gametogencsis docs not proceed past the first stage in meiosis. Synapsis of homologous chromosomes from the two parent species evidently does not occur because of differences in morphology.