ABSTRACT
Cell proliferation is dependent on a complexprocess of cell division known as mitosis, compris ing karyokinesis (nuclear division) and cytokinesis (division of cell cytoplasm). It is the only event in the life cycle of a cell readily distinguishable in the light microscope. Chromatin, composed of gene-bearing DNA, is dispersed in the nucleoplasm at rest. The chro mosomes become visible in early mitosis as discrete threads of condensed chromatin. There are 22 num bered pairs of autosomes, i.e. homologous chromosomes in human cells; plus two sex chromosomes, either XY in males, or XX in females (Figures la, b, c).