In Interphase, after cell division the cell grows to it’s regular size and carries out its usual functions, synthesising lots of substances, mainly proteins, in the process. At some time during the interphase, a signal might be received that the cell should divide again. The DNA in the nucleus replicates to make each chromosome consist of two identical chromatids, each with a copy of the cell’s DNA.
The process of nuclear division follows the interphase. It is a continuous process. This takes part in four phases: prophase, metaphase, anaphase and telophase.
In the following example only four chromosomes are shown to make the diagram clearer. And male and female chromosomes are distinguished by their colour. This is an animal cell, but the activities of the chromosomes in plant cells are the same. After nuclear division the cell usually divides into two cells with infolding of the cell surface membrane, in animal cells, or the formation of a new cell wall and cell surface membrane, in plant cells.
Prophase
In prophase the chromosomes condense becoming shorter and thicker, they become more noticeable because they stain more strongly. The centrioles duplicate and move towards the poles, and spindles begin to form.
Metaphase
In Metaphase the nuclear envelope breaks down and, ‘disappears’ (breaks up into small vesicles). The centriole pairs reach the poles and the spindles are completely formed. The Chromosomes continue to condense. Microtubules of the spindle attach to the centromeres of the chromosomes; they pull on the centromere arranging the chromosomes on the equator.
Anaphase
In Anaphase the links between the sister chromatids break and the centromeres of the sister chromatids move apart pulled by microtubules of the spindle.
Telophase
In Telophase sister chromatids, which are now effectively separate chromosomes, reach opposite poles, the chromosomes decondense and nucleolus begins to reappear. The nuclear envelope appears and the spindle disappears.
