Meiosis

• What is meiosis cell division?

  • Produces daughter cells that are genetically different from each other
  • two nuclear divisions
  • creates 4 haploid daughter cells
• What is independent segregation?

  In meiosis 1, homologous pairs of chromosomes line up opposite at the equator.

  It is random which side of the equator the paternal and maternal chromosomes lie.

  The pairs separate, so one of each homologous pair of chromosomes ends up in daughter cell.
• What is the result of independent segregation?

  • Creates a large number of possible combinations of chromosomes in the daughter cells produced.
  • This can be calculated using 2n, where n=number of homologous pairs.
  • In humans there are 8,388,608 possible combinations of chromosomes.
• What is crossing over?

  • When homologous pairs line up opposite each other at the equator, parts of chromatids become twisted around each other, creating a structure called chiasma.
  • This puts tension on the chromatids, causing pairs of the chromatid to break.
  • The broken parts of the chromatid recombine with another chromatid.
  • This results in new combinations of alleles.
• What are the differences between meiosis and mitosis?

  • Meiosis- 2 nuclear divisions, produces 4 haploid cells, introduces genetic variation.
  • Mitosis- 1 nuclear division, produces 2 diploid cells, creates genetically identical cells
• What causes a final increase in genetic variation?

  • Random fertilisation further increases genetic variation
  • (2^n)^2 possible combinations of chromosomes when you consider random fertilisation.
  • For humans- (2^23)^2=7.04x10^13 (before crossing over is considered)