3.24 Mitosis

3.24 Understand that division of a diploid cell by Mitosis produces two cells which contain identical sets of chromosomes

What is Mitosis?
Mitosis is a form of cell division that results in the increase in the number of cells.

Outline:

1. Begin with a single cell
• The number of chromosomes in this original cell is referred to as its Diploid number (2n)
• All animals have a different Diploid number (Humans, 2n = 46)
2. The cell divides into two daughter cells
• These cells are identical to the mother cell
• 1. Each of these cells has a Diploid nucleus (the same number of chromosomes as the mother cell)
• 2. They have the same set of chromosomes as each other

How are the copies of chromosomes made?

DNA replication

1. The process takes place inside the nucleus while it is still intact; before any separation has gone underway. This resting stage is known as the interphase stage of the cell cycle
2. Each chromosome undergoes a copying process to form an identical copy of itself
• It has all the same Genes and Alleles
3. These two copies are held together by a structure around the centre by what’s called a centromere.
4. These two chromosomes held together by a centromere are referred to as a pair of chromatids

How do they separate?

Cell Division

1. The first sign a cell is entering mitosis is when we see the breakdown of the nuclear membrane (this is known as the Prophase)
1. The chromosomes then become visible as a pair of Chromatids
2. A network of Protein molecules (the Spindle and Spindle fibres) extend from one pole of the cell to the other (this is the Late Prophase)
3. The pair of chromatids work their way towards the middle of the spindle and join onto a spindle fibre by the centromere (the Metaphase)
4. The Anaphase is where the spindle fibre shortens to pull each chromatid in an opposite direction and ultimately they ultimately separate and each one will rest in the opposing poles.
5. The final phase is known as the Telophase when the nuclei begin to reform around the chromatids at each pole of the cell. There are now two nuclei
6. And finally a phase called the Cytokinesis is where the cell splits in two, but this particular stage is not regarded as part of the Mitosis Cycle.

The image below visually explains the process