Mitosis

• What is mitosis?


  The division of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell. The daughter cells are genetically-identical to the parent cells.
• What are the four stages of mitosis?

  Prophase, metaphase, anaphase, telophase.
• What happens during prophase?

  • Chromosomes first become visible
  • Centrioles move to the opposite ends (poles) of the cell
  • Spindle fibres develop from each of the centrioles
  • These spindle fibres form the spindle apparatus
  • (Plant cells do not have centrioles, but still develop a spindle apparatus)
  • Nucleolus disappears and nuclear envelope breaks down
  • Chromosomes are free in the cytoplasm of the cell
  • Chromosomes are drawn towards the equator of the cell by the spindle fibres attached to the centromere (join between chromosome and copy)
• What is the structure of a chromosome?


  As below:

  
• What happens during metaphase?

  • Chromosomes are made up of two chromatids
  • Each chromatid is an identical copy of DNA from the parent cell
  • Chromatids are joined by the centromere
  • Microtubules from the poles attach to the centromere
  • Chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell
• What happens during anaphase?

  • Centromeres divide into two
  • Spindle fibres pull the individual chromatids apart
  • The chromatids move to opposite poles and are now called chromosomes.
  • The energy for this is provided by mitochondria, which gather around spindle fibres
  • If the cells are treated with chemicals that destroy the spindle, the chromosomes remain at the equator.
• What is the primary function of mitosis in organisms?

  Mitosis produces daughter cells that are genetically identical to the parent cells.
• Why is it essential to make exact copies of existing cells?


  It is essential for growth, repair, and reproduction.
• What happens when two haploid cells fuse together?

  They form a diploid cell with all the genetic information needed to form a new organism.
• How does mitosis contribute to the resemblance of a new organism to its parents?

  Mitosis ensures that all cells growing from the original diploid cell are genetically identical.
• Why is repair an important function of mitosis?

  It is important that new cells produced have an identical structure and function to the ones that have been lost.
• How do single-celled organisms reproduce?

  Single-celled organisms divide by mitosis to give two new organisms.
• What is the genetic relationship between the offspring and the parent organism in mitosis?

  Each new organism is genetically identical to the parent organism.
• What are the advantages and disadvantages of having offspring that are genetically identical to their parents?

  Advantages:

  • Uniformity in traits
  • Successful traits are preserved

  
  

  Disadvantages:

  • Lack of genetic diversity
  • Vulnerability to environmental changes
• What happens during telophase?

  • Chromosomes reach their respective poles
  • They become longer and thinner, before disappearing
  • This leaves widely spread chromatin
  • The spindle fibres disintegrate
  • The nuclear envelope and nucleolus reform