Chromosomal aberrations in embryos from overripe eggs

Abstract

Overripeness in eggs of Rana pipiens was obtained by keeping postovulatory females at room temperature and delaying fertilization 3–5 days. In Xenopus laevis similar results were attained by delaying ovulation. About 80 crippled embryos, issued from overripe eggs that were used for chromosomal studies, had reached prefeeding stages ranging from 20 to 24. By this time the most severely abnormal individuals had already died, but also the majority of those studied would probably not have been able to survive until metamorphosis. Some malformed embryos still have normal chromosome complements, but the majority show deviations which are classified as meiotic, ploidic, and cleavage types. It is concluded that overripeness of the egg is an important cause of chromosomal nondisjunction in meiotic and in mitotic divisions. No definite relationship between the type of chromosomal deviation and the morphologic character of malformations has been established, so far.