Micronucleus formed during mitotic cell division and present in the cytoplasm of daughter cells near the nucleus. The main mechanisms contributing to their creation are chromosome breakage and dysfunction of the mitotic apparatus. Micronuclei may contain whole chromosomes or chromatids, acentric fragments and chromatid fragments. Observed changes in the incidence of micronuclei and content depending on the disease, the aging process, and different environmental factors.