It takes many cell divisions to make a person from a single celled egg. In each of those divisions all the genes must be replicated and passed to each daughter cell. For the remainder of this lecture we will concentrate on the process of cell division mitosis and on the structures known as chromosomes . Within a tissue which is growing individual cells each go through a regular pattern of growth and division known as the cell cycle. There are many interesting features of the cell cycle from, for instance, a cancer biologist's viewpoint, concerned with the regulation of cell division.
Cancer is, after all, a disease of unregulated cell division.
From our perspective as geneticists we can take a simplified view of the process and concentrate solely on that part of the cycle which actually takes the least time, the mitotic division. Interphase Into this phase we can lump all the important events which we are not going to consider. The act of mitosis can be conveniently divided into four phases. The replicated chromosomes become visible and can be seen to be comprised of two sister chromatids still joined together at the centromere , the nuclear membrane breaks down, centrioles move to opposite poles and the spindle forms between them. The chromosomes are now at their most condensed.