B2(iii) - Genetics 3.

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Cell Division - Meiosis.

Gametes Have Half the Usual Number of Chromosomes.

1) During sexual reproduction, two cells called gametes (sex cells) combine to form a new identical individual.

2) Gametes only have one copy of each chromosome. This is so you can combine one sex cell from the mother and one sex cell from the father and still end up with the correct number of chromosomes in the body cells.

3) For example human body cells have 46 chromosomes. The gametes have 23 chromosomes each, so that when an egg and sperm combine, you get 46 chromosomes again.

Meiosis Involves Two Divisions.

To make new cells which only have half the original number of chromosomes, cells divide by meiosis. In humans it only happens…

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