The significance of meiosis

• Significance of Meiosis


  • Having genetically different offspring can be advantageous for natural selection
  • Meiosis has several mechanisms that increase the genetic diversity of gametes produced
• Crossing over


  1. Homologous chromosomes pair up and are in very close proximity during meiosis I

  2. Non-sister chromatids can cross over and get entangled

  3. Crossing points are called chiasmata

  4. Stress on DNA molecules causes a section of chromatid from one chromosome to break and rejoin with the chromatid from the other chromosome

  5. Swapping of alleles results in new combinations
• There is usually at least one, if not more, chiasmata present in each bivalent during meiosis
• Crossing over is more likely to occur


  Further down the chromosome away from the centromere
• Independent assortment


  1. Homologous pairs align randomly along the equator of the spindle during metaphase I

  2. Orientation of one homologous pair is independent/unaffected by the orientation of any other pair

  3. Homologous chromosomes are then separated and pulled apart to different poles

  4. Combination of alleles in each daughter cell depends on how the pairs of homologous chromosomes were lined up
• The formula 2^n can be used to work out the number of different possible chromosome combinations, where n corresponds to the number of chromosomes in a haploid cell
• For humans this is 2^23 which calculates as 8,388,608 different combinations
• Meiosis creates genetic variation between the gametes produced by an individual


  Through crossing over and independent assortment
• During fertilization, any male gamete can fuse with any female gamete to form a zygote


  This random fusion of gametes creates genetic variation between zygotes as each will have a unique combination of alleles
• There is an almost zero chance of individual organisms resulting from successive sexual reproduction being genetically identical