Origins of Heteroploidy in Chicken Embryos

Abstract

INTRODUCTIONIn man and the agriculturally important ungulates 25 to 40% of fertilized eggs do not result in living, healthy young. Losses occur as early embryonic deaths, abortions, stillbirths, or deaths of neonates. Most of the loss occurs at early developmental stages, i.e., as early embryo death. It is now known, at least in man, that the most important single cause of this reproductive wastage is the occurrence of anomalous chromosome complements of the affected embryos. Zygotes with fewer or more chromosomes than the number characteristic for the species possess an unbalanced genome the effect of which, in most instances, is to throw the developmental process off its normal course. Death or severe physical functional impairment is the outcome.In birds, too, errors of meiosis, fertilization, or early cleavage divisions result in embryos bearing anomalous chromosome complements. Most of these embryos do not survive incubation. A relatively large segment of .