Modifications of Mitosis

Abstract

Although normal mitosis is characterized by the regular alternation of chromosome reproduction and segregation of daughter chromosomes, the two processes are not necessarily correlated, and their relationship can be changed in different ways (cf. Oksala, 1954). As a rule, such modifications lead to a chromosome constitution differing from the basic complement of the individual (Fig. XII.1). Apart from multipolar mitoses, all other mitotic modifications are characterized by an absent or defective spindle, and in most cases these result in the duplication of the chromosome number (Fig. XII.2). Nagl (1978) has united the most important of these mechanisms, endoreduplication and endomitosis, under the term endocycles. The terminology referring to mitotic modifications has been the subject of considerable dispute. I shall use that proposed by Levan and Hauschka (1953), since it is established in the literature.