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
Examiner 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.
