The Outcomes & Processes of Mitosis & Meiosis (AQA A Level Biology)

Understanding the Outcomes & Processes in Mitosis & Meiosis

• Mitosis and meiosis are both forms of cell division

• They have many similarities and differences that are important for their function

• Mitosis contributes to the growth of an organism or to replace dead/dying cells

• Meiosis produces genetically different gametes for sexual reproduction

The Different Outcomes of Mitosis and Meiosis

• Number of daughter cells

  • Mitosis = 2

  • Meiosis = 4

• Ploidy of daughter cells

  • Mitosis = 2n

  • Meiosis = n

• Are the daughter cells genetically identical to the parent cells and each other?

  • Mitosis = yes

  • Meiosis = no

Chromosome Content After Divisions

• The chromosome content of a cell changes throughout mitotic and meiotic divisions

• Mitosis ends with two daughter cells genetically identical to each other and the parent cell

  • This is important so that growth and cell replacement can occur within a body continually

  • Every cell in an organism's body (other than gametes) contain exactly the same genetic material - the full genome

• Meiosis ends with four daughter cells all of which contain half the genetic material of the parent cell and are all different from each other and the parent

  • This is important for genetic variation within families and the population

  • Genetic variation can reduce the risk of inheriting genetic diseases

Image showing how the chromosome content changes during the mitosis and meiosis

The Random Fertilization of Gametes Increases Genetic Variation

• Meiosis creates genetic variation between the gametes produced by an individual through crossing over and independent assortment

• This means each gamete carries substantially different alleles

• During fertilization, any male gamete can fuse with any female gamete to form a zygote

• This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles

• Zygotes eventually grow and develop into adults

• The presence of genetically diverse zygotes contributes to the genetic diversity of a species

Image showing how meiosis and the random fusion of gametes affects genetic variation