Inheritance

• 23 pairs of chromosomes.
• 22 cases - each chromosome in the pair is a similar shape and has genes carrying information about the same things.
• The one pair that is different is the sex chromosome.
• X X chromosome - you are female.
• X and much smaller y chromosome - you are a boy.

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Genetics - the study of inheritance

At FERTILISATION the nucleus of the sperm joins with the nucleus of the egg.

The nucleus contains thread-like CHROMOSOMES that carry the GENES that control all your characteristics.

Mitosis - is the division of body cells to produce new cells. Mitosis occurs....

• for growth
• for repair
• in asexual reproduction

Meiosis - is the division of sex cells. Body cells contain 46 chromosomes arranged as 23 pairs.

Gametes are sex cells, i.e. female eggs and male sperm. Gametes have 23 chromosomes (one from each pair).

The fusion of two gamete cells produces a zygote. A zygote has 46 chromosomes in total (23 pairs).

So the 23 pairs from a sperm join to the 23 pairs from an egg to form the embryo.