Meiosis

• Meiosis


  A form of cell division that gives rise to genetic variation
• Meiosis


  • Main role is production of haploid gametes and maintenance of chromosome number
  • Cells produced have half the number of chromosomes (reduction division). Produces genetically different cells.
• Genetic Variation


  1. Crossing over - exchange of sections of DNA between homologous chromosomes

  2. Random fusion of gametes

  3. Independent assortment - various combinations of maternal and paternal chromosomes distributed between two daughter cells
• Chromosome mutations


  Changes to the structure or number of chromosomes (causing aneuploidy)
• Types of chromosome mutations

  • Translocation
  • Duplication
  • Deletion
  • Inversion
• Translocation (swapping of genes, not between alleles in a homologous pair). It involves breaking off one chromosome and joining to another, can be balanced or unbalanced
• Aneuploidy


  Happens as a result of non-disjunction, where either homologous chromosomes or sister chromatids fail to separate
• Results of aneuploidy


  • More than two chromosomes in a pair (polysomy) - e.g. Down's Syndrome (trisomy 21)
  • Less than two chromosomes in a pair (monosomy) - e.g. Turner's Syndrome (monosomy of sex chromosomes)