Meiosis and Genetic Variation

• Types of mutation


  • Chromosome mutation
  • Gene mutation
• Independent segregation


  Occurs during Metaphase I of meiosis
• Crossing over


  Occurs during Prophase I of meiosis
• Sources of genetic variation

  • Crossing over
  • Independent segregation
  • Random fertilisation
• Chiasmata


  The section where chromatids cross over, break and rejoin with its homologous partner
• Formula for calculating possible chromosome combinations

  2^n, where n = the number of pairs of homologous chromosomes
• Crossing over


  1. Chromatids of each pair become twisted around another

  2. Tension is created & portions of the chromatids break off

  3. Broken portions might rejoin with chromatids of its homologous partner (recombination)
• Crossing over produces new genetic combinations of maternal and paternal alleles
• Independent segregation


  1. Chromosomes line up alongside their homologous partner

  2. When chromosomes align it is random

  3. One of each pair passes to each daughter cell
• Homologous chromosomes


  A pair of chromosomes, one maternal and one paternal, that have the same gene loci
• Allele


  One of the different forms of a particular gene
• Locus


  The position of a gene on a chromosome or DNA molecule
• Gene


  A base sequence of DNA that codes for the amino acid sequence of a polypeptide AND a functional RNA product OR ribosomal RNA (rRNA) OR transfer RNA (tRNA)
• Meiosis halves the number of chromosomes and produces genetic variation among offspring
• Second meiotic division


  1. Chromosomes move apart

  2. Four cells have been formed at the end of meiosis 2
• First division of meiosis

  1. Homologous chromosomes pair up and their chromatids wrap around each other

  2. Equivalent portions of chromatids exchange by 'crossing over'

  3. Homologous calls have separated with one chromosome from each pair going into one of the two daughter cells
• Meiosis involves two nuclear divisions
• The result of meiosis is 4 daughter cells, each with half the number of chromosomes as the parent cell