Crossing over in chromosomes

• During meiosis 1 when homologous chromosomes line up together at the equator next to each other there is a possibility that parts of the chromosome can swap places with the other homologous pair

  • This means that alleles that we may not have independently assorted can now end up in different gametes
• Crossing over: (after homologous chromosomes line up together)

  1. The chromatids of each pair become twisted around each other
  2. Tensions created and portions of chromatids break off
  3. These broken portions might then rejoin with the chromatids of its homologous partner
  4. In this way new genetic combinations of maternal and paternal alleles are produced
• The process is known as crossing over because the chromatids cross over one another many times
• The broken-off portions of chromatid recombine with another chromatid, so this process is called recombination
• Chiasma - The point where the chromosomes break
• Recombinant - Chromatids which have swapped sections with others
• How crossing over leads to increase in genetic variation:

  • Crossing over leads to the exchange of alleles between homologous chromosomes
  • This recombines alleles that wouldn't normally be found on the same chromosome and inherited together in gametes
• The closer together the loci are on the chromosome and the closer they are to the centromere, the lower the chance of a chiasma forming between them to separate them

  • This information can give an indication of how close two genes are on a chromosome