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).