AQA AS Biology

Revision Notes

4.3.7 The Outcomes & Processes of Mitosis & Meiosis

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

Chromosome content, downloadable AS & A Level Biology revision notes

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

Random fusion of gametes, downloadable AS & A Level Biology revision notes

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

Exam Tip

It is common for a question to ask you to identify where meiosis is occurring in an unfamiliar life cycle. There is a helpful trick for this, meiosis always involves a  reduction division. This is a nuclear division that reduces the chromosome number of a cell. So when the ploidy of the cell is halved it can be said that meiosis has just occurred.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top