AQA A Level Biology复习笔记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

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

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.

 

转载自savemyexams

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