Meiosis and genetic variation

• Genetic variation is increased during meiosis by crossing over and the independent segregation of homologous chromosomes. Apart from mutations, explain one other way genetic variation within a species is increased.


  Random fertilisation; new allele combinations (new maternal and paternal chromosome combination)
• During meiosis 1, chromosomes that carry the same genes pair up. These pairs are called homologous chromosomes
• What happens during meiosis 2?

  the sister chromatids move apart from each other to form two pairs of daughter cells
• describe how crossing over in meiosis leads to genetic variation

  During meiosis 1, homologous chromosomes twist around each others. Portions of chromatids are exchanged which produces new combination of alleles in each chromosome
• Describe how independent segregation in meiosis leads to genetic variation

  • homologous chromosomes line up at random
  • creates different combinations of alleles
• Describe how non-disjunction leads to genetic 


  • in meiosis 1, non disjunction can stop homologous pairs of chromosomes from separating
• Describe how non-disjunction leads to genetic

  • in meiosis 1, non disjunction can stop homologous pairs of chromosomes from separating
  • in meiosis 2, it can stop sister chromatids from separating
  • both result in gametes with unequal number of chromosomes
• what is the formula for the number of chromosome combinations that can occur after random fertilisation

  $(2^n)^2$