Meiosis

• What gametes are produced during meiosis cell division?

  • Sperm and egg
• What is a haploid?

  • It only contains one chromosome of each homologous pair.
• What is a diploid?

  • It contains two chromosomes from each homologous pair.
• What's the purpose of meiosis?

  • Genetically different gametes allow for natural selection which ensures the survival of species which is only possible with variation.
  • The halved number of chromosomes in gametes allows for the restoration of the diploid number at fertilisation.
• What is the principle of independant segregation?

  • It's a genetic principle stating that the alleles of two genes will segregate into daughter cells independently of each other
• What's the difference between mitosis and meiosis?

  • There's one division in mitosis and two in meiosis.
  • Cells are genetically identical in mitosis, cells are genetically different in meiosis.
  • Crossing over only occurs in meiosis.
  • Diploid to diplod/haploid to haploid in meiosis, diploid to haploid in meiosis.
• What happens during crossing over?

  • Homologous pairs form chiasmata where chromatids twist together.
  • The exchange of alleles between homologous pairs of chromosomes during crossing over produces new coombinations of alleles.
• Why can't a mule (63 chromosomes) reproduce?

  • If a cell has an odd number of chromosomes it must be haploid as diploid cells have 2 sets of chromosomes and so their total must be an even number of chromosomes.
  • Due to this an organism that has an odd number of chromosomes must be sterile as during meiosis chromosomes pair up and then separate into different cells.
  • In organisms with an odd number of chromosomes, it becomes impossible for each chromosome to find a partner during meiosis.
• What are the benefits of mitosis?

  • There are fewer stages so the process is quicker requiring less energy.
  • Only one parent is needed to colonise a new environment.
  • Produces clones so a successful genotype is maintained.
  • We can identify fertilisation as it's haploid to diploid.
• What are the benefits of meiosis?

  • It introduces genetic variation resulting in a greater chance of survival for a species.
  • We can identify meiosis as it's diploid to haploid.
• If the number of chromosomes goes from 8 to 16 what has occured?

  • Fertilisation has occured as the number of chromosomes has doubled.
• If the number of chromosomes goes from 8 to 8 what has occured?

  • Mitosis has occured as the number of chromosomes has stayed the same.
• If the number of chromosomes goes from 16 to 8 what has occured?

  • Meiosis has occured as the number of chromosomes has halved.