Gametes, Meiosis and Fertilisation

Gametes, Meiosis and Fertilisation

CellsGametes are sex cells which are produced in the reproductive organs.

  • females produced eggs in their ovaries
  • males produce sperm in their testes

As you’ve already seen, body cells contain two sets of chromosomes. Gametes only have one set. This is because they’re formed by a process called meiosis.


  • When a cell divides by meiosis copies of the genetic information are made.

However, then the cell divides twice thereby creating four gametes each of which contains only one set of chromosomes



When a sperm and an egg fuse together this process is known as fertilisation. Each gamete contains half the amount of genetic material required to create an offspring. However, once they’ve fused together the resulting cell, known as a zygote, has the right amount and begins to divide by mitosis. A new individual can now be formed.

Asexual reproduction is very common in plants and very rare in animals. In comparison to sexual reproduction, the cells of the offspring are created by mitosis from the parental cell. This means that their cells contain the same alleles as that of their parents.

NOTE: You don’t have to know all the stages of mitosis or meiosis.


Embryo screening

Embryo screening can be carried on embryos to see if they have genetic disorder such as polydactyl or cystic fibrosis. However, there are ethical fears over the fact that society could be heading towards ‘designer babies.’

NOTE: You don’t need to be aware of any techniques for embryo screening.