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Meiosis

Meiosis

  • This is the type of cell division used to make gametes. Gametes are sex cells, which are ova in females and sperm in males. During sexual reproduction, two gametes combine to form a new cell which will grow to become a new organism.
  • Gametes are haploid, which means they only have one copy of each chromosome. This is so when the two gametes fuse during fertilisation, the zygote has the correct number of chromosomes.

Process

  • Meiosis only occurs in reproductive organs. Four haploid nuclei are produced whose chromosomes are not identical.
  • Two divisions occur during this process.

Division 1

  • As with mitosis, the cell duplicates its DNA.
  • The chromosome pairs line up in the centre of the cell.
  • The pairs of chromosomes are pulled apart so each new cell only has one copy of each chromosome. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell.
  • Each new cell will have a mixture of the mother’s and father’s chromosomes. Mixing up the alleles in this way creates variation in the offspring. This is a huge advantage of sexual reproduction over asexual reproduction.

Division 2

  • In the second division the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.

Four haploid gametes are produced, each with only a single set of chromosomes in it.