Chromosome behaviour in mitosis

Chromosome Behaviour in Mitosis

Prophase

  • Mitosis starts with prophase. The tightly coiled DNA begins to become visible as each individual chromosome.
  • Chromosomes condense becoming shorter and thicker which makes them easier to move. Each chromosome is composed of two identical sister chromatids joined at a region called the centromere.
  • The nucleolus disintegrates and the nuclear envelope breaks down, releasing chromosomes into the cytoplasm.
  • Spindle fibres begin to form from structures known as centrosomes. These centrosomes move toward opposite poles of the cell.

Prometaphase

  • In prometaphase, the chromosomes are fully condensed and spindle fibres interact with the chromosomes.
  • Some spindle fibres attach to the centromeres of the chromosomes via a region called the kinetochore.

Metaphase

  • During metaphase, the fully condensed chromosomes align along the cell’s midway point in a formation known as the metaphase plate.
  • Each chromosome is held in place by spindle fibres attached to the kinetochore regions on both sides of the centromere.

Anaphase

  • Anaphase begins when the centromeres holding the sister chromatids together split.
  • Spindle fibres attached to the kinetochores pull the sister chromatids, now individual chromosomes, towards opposite poles of the cell.
  • Consequently, the cell elongates.

Telophase and Cytokinesis

  • Telophase features the formation of a nuclear envelope around the set of chromosomes at each pole. The chromosomes then decondense and return to their uncoiled state.
  • Following telophase, the cytoplasm divides, a process known as cytokinesis. Each new cell contains a complete set of the organism’s chromosomes.

Significance of Chromosome Behaviour During Mitosis

  • The specific and systematic behaviour of chromosomes ensures that each daughter cell receives an identical set of chromosomes.
  • This is crucial as it maintains the phenotype and genetic stability from one generation to the next. Any inconsistency can lead to issues such as cancer or other genetic aberrations.

Remember to regularly consult a karyotype to understand the behaviour and constitution of chromosomes. This can be a vital tool when tackling topics on mitosis and meiosis.

Revision Tip: Try using diagrams as a tool for visualising the steps of mitosis. Drawing the progression of chromosome behaviour will help you remember the stages and their particularities.