Mitosis

MITOSIS:

• Is a division of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell.
• Except in the rare event of a mutation, the genetic make-up of the 2 daughter nuclei is also identical to that of the parent nucleus.
• Mitosis is always preceded by a period during which the cell is not dividing.
• This period is called interphase.
• It is a period of considerable cellular activity that includes a very important event, the replication of DNA.
• The 2 copies of DNA after replication remain joined at a place called the centromere.
• Although mitosis is a continuous process, it can be divided into 4 stages:
  • Prophase:
    • The chromosomes first become visible, intially as long thin threads, which later shorten and thicken.
    • Animal cells contain 2 cylindrical organelles called centrioles, each of which moves to opposite ends (called poles) of the cell.
    • From each of the centrioles, spindle fibres develop, which span the cell from pole to pole.
    • Collectively, these spindle fibres are called the spindle apparatus.
    • As plant cells lack centrioles but do develop a spindle apparatus, centrioles are clearly not essential to spindle fibre formation.
    • The nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm of the cell.
    • These chromosomes are drawn…