Abstract
Micronuclei originate from chromatin which for different reasons has been lagging in anaphase (Fig. la-d). In the course of telophase this material is included into one or the other daughter cell where it either can fuse with the main nucleus or form one or several secondary nuclei. These are, as a rule, considerably smaller than the principal nucleus and are therefore called micronuclei. Lagging has two main causes: chromosome breakage and malfunction of the spindle apparatus. In the first case the lagging elements are acentric chromosome fragments and di- or multicentrics connected by bridges, and in the second case they consist of entire chromosomes.
Schmid, Werner