Meiosis

• Meiosis produces four daughter cells, each with half the number of chromosomes as the parent cell
• Meiosis produces daughter cells that are genetically different from each other
• In sexual reproduction two gametes fuse to give rise to new offspring

  • In order to maintain a constant number of chromosomes in the adults of a species, the number of chromosomes must be halved at some stage in the life cycle - this halving occurs as a result of meiosis
• Meiosis is nuclear division that results in four cells that have half the DNA (n) of the original organism (2n)

  • This is to produce gametes which can then take part in sexual reproduction
• Meiosis allows for the fusing of two haploid nuclei to restore the full number of chromosomes and make a diploid nucleus
• Meiosis also introduces genetic variation by producing a new unique organism with a different combination of alleles from each parent
• Allele - Different versions of the same gene

  • They code for the same protein but different forms
• Every diploid cell of an organism has two complete sets of chromosomes: one set provided by each parent
• During meiosis, homologous chromosomes separate, so that only one chromosome from each pair enters a daughter cell

  • This is known as the haploid number of chromosomes which, in humans, is 23
  • When two haploid gametes fuse at fertilisation, the diploid number of chromosomes is restored
• Homologous chromosomes - Two chromosomes that carry the same genes but not necessarily the same alleles of the genes
• Gene - A length of DNA that codes for a polypeptide
• Locus - The position of a gene on a chromosome or DNA molceule
• Allele - One of the different forms of a particular gene
• Homologous chromosomes - A pair of chromosomes, one maternal and one paternal, that have the same gene loci