Heterosis in Poultry

NEWCOMER (1957) presented evidence that the somatic chromosome number of the fowl is 6 pairs rather than 18 or 38 as formerly supposed. To account for the difference, he proposed that there are a variable number of heterochromatic elements or chromotoid bodies which he designated as “chromosomoids.” During the course of meiosis, these chromosomoids may undergo fusion or fragmentation, and frequently they have been counted erroneously as chromosomes when they are fused. Newcomer suggested that the chromosomoids apparently function as reserves of nucleo-proteins for chromosome duplication. Newcomer's work on the cytology of the fowl is of special interest to breeders and geneticists, because only 6 linkage groups have been reported in the fowl. If the fowl has but 6 pairs of chromosomes, then roughly speaking we might suppose that ⅙ of the heredity of the fowl is associated with the sex chromosomes. Thus the fact that relatively many more sex …