AQA A Level Biology复习笔记4.3.7 The Outcomes & Processes of 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