3.24

3.24a
Mitosis –form of cell division, which results in growth (growth = increase in number of cells)
The number of chromosomes in a nucleus is known as the Diploid number (2n)
i.e 2n= 46 human 2n=38 cats
During the process of mitosis the cell will divide to become two cells, each with a nucleus. Inside the nucleus they each have a ‘diploid nucleus’, he cells are identical (aka daughter cells)
Identical because they have the same number of chromosome and they also have the same set of chromosomes (a chromosome from one cell will have an identical chromosome in the other cell)



3.24b
How are copies of chromosomes made and how do they separate into the two cells?

The split cells have the same number of chromosomes and same set of chromosomes.
The first cell has to copy its chromosomes to produce another set for the second cells. This process is called DNA replication. In this process each chromosomes undergo a copying process to form an identical copy of itself, with all the same jeans and alias. These two copies are held together around the center region by a structure known as a centromere (“pair of chromatids”)
Takes place in the cell nucleus; this is known as the Interphase of the cell cycle.



3.24c
Stages of Mitosis
During the phase of interphase is when the DNA replication occurs.
The first sign that a cell is entering the process of mitosis is when we see the breakdown of the nuclei membrane, known as the Prophase. The chromosomes become visible as a pair of chromatids.
A network of protein molecules known as the spindle and the spindle fibers extend from one pole of the cell to the other.
Late Prophase: the pair of chromatids will move towards the spindle and will join onto one of the spindle fibers at the centromere.
Metaphase: Chromatids are in the middle arranged across the equator of the cell attached to the spindle fibers connected by the centromere.
Anaphase: the spindle fibers shorten, pulling on chromatid in one direction and the other in the other direction, separated the ‘pair of chromatids’. They move to the poles of the cells
Telophase: The nucleus begins to reform around the chromosomes at the end of the cell. This will be the new nucleus of the new cell.
Cytokinesis: The cell splits into two. This is NOT part of Mitosis (it’s what happens after). The cell moves inwards, dividing the cytoplasm in half and the membrane will fuse across the equator to form the two cells. (In a human 23 pairs of chromosomes are separated).