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Plant and animal bodies consist of millions of eukaryotic cells. These cells have their genetic material DNA bound with histone proteins in chromosomes. These chromosomes are enclosed in a nucleus. These cells under go the processes of mitosis and meiosis.

Revision sites

• GCSE for mitosis and meiosis

• Mitosis and meiosis compared
  

The body cells are diploid as they possess pairs of homologous chromosomes. One of each pair is derived from the mother and one is derived from the father.
Gametes (sperm and egg) are haploid, as they contain only one of each pair of chromosomes. Fusion of these gametes at fertilisation produces a diploid cell, the zygote. This then divides by mitosis to produce all the cells of the body.
When cells divide they undergo a cycle of events called the cell cycle.

Each phase consists of

1. a non-dividing phase or interphase which is subdivided into; a growth phase (G 1); a replication phase (S); and a second growth phase (G2) when proteins are made which are necessary for division.
   Mitosis which is division of the nucleus. It results in the formation of two daughter nuclei which are genetically identical and have the same number of chromosomes as the parent.
   
2. Cytokinesis during which the cytoplasm divides to produce two daughter nuclei.

Mitosis is important in asexual reproduction, in the production of clones and in growth and body repair. The stages of mitosis are clearly demonstrated in the onion root tip. -

Meiosis - is responsible for the production of gametes. It is a complex process that involves two cell divisions. Meiosis contributes to the production of variety in offspring produced by sexual reproduction through the processes of crossing over and independent assortment. There is also a reduction in the number of chromosomes to produce the haploid number. This is necessary to restore the diploid number in a new individual.

Quizzes

Try these quizzes on mitosis - and meiosis -

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• OSFC Quiz 1 on Mitosis and Meiosis
• OSFC Quiz 2 on Mitosis and Meiosis
• OSFC Quiz 3 on Mitosis and Meiosis
• OSFC Quiz 4 on Mitosis and Meiosis