A level Biology exam revision resources written by A level Examiners


This type of cell division produces two genetically identical daughter cells from one parent cell. Mitosis is a continuous process with no pauses, but for descriptive purposes it is commonly divided into four stages:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

The time taken for all four stages to occur varies, though it is usually between - 3 hrs.


During prophase the chromatin condenses, and chromosomes become visible as long, thin entangled threads which become shorter and thicker. The Nucleolus disappears. Centrioles begin to migrate to opposite poles. As they move apart a network of protein microfilaments develops between them (this is the spindle). Towards the end of prophase the nuclear membrane breaks down.

Figure 3 : Cell towards the end of prophase



During metaphase the chromosomes now can be seen to consist of two chromatids joined at a centromere (see figure 4 below). The two chromatids of each chromosome are called sister chromatids. Chromosomes arrange themselves on the equator of the spindle. The chromosomes attach to spindle by their centromeres

Figure 4


The figure 5 shows a cell during metaphase.

Figure 5



Anaphase is the shortest phase of mitosis. Sister chromatids separate and move to opposite poles. The chromatids move along the spindle fibres..   Exam Advice

When looking at these chromatids and chromosomes it is vital to realise that one chromatid is an identical copy of the other. The copy was made during the S phase of interphase. When a chromosome splits into two chromatids, each chromatid still contains all the genes the chromosome contained. So when chromatids go to different poles of the cell each pole still has the same number of chromosomes as the original cell.

Figure 6 : Cell during Anaphase



The separated chromatids are now referred to as chromosomes. On reaching the poles they begin to unwind. A nuclear membrane then forms around the bundles at each pole. The chromosomes continue uncoiling and a nucleolus reappears at each pole. This re-establishes the appearance the nucleus had during interphase.

The figure 7 shows a cell during telophase. The left hand diagram is early telophase, and the right hand picture is late telophase.

Figure 7 : Telophase



Soon after nuclear division is complete the cytoplasm separates into two, forming two separate cells.


The two daughter cells produced are identical in chromosome number and genetic make-up to the parent cell. This ensures that the genetic information is the same in the nuclei of all the cells of an organism.

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