• Mitosis is the process of nuclear division by which?two genetically identical daughter nuclei?are produced that are also genetically identical to the parent cell nucleus (they have the same number of chromosomes as the parent cell)
• Although mitosis is, in reality, one continuous process, it can be divided into?four main stages
• These stages are:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

   

• Most organisms contain many chromosomes in the nuclei of their cells (eg. humans have 46) but the diagrams below show mitosis of an animal cell with only four chromosomes, for simplicity
• The different colours of the chromosomes are just to show that half are from the female parent and half from the male parent

Prophase

• Chromosomes?condense?and are now visible when stained
• The chromosomes consist of?two identical chromatids?called?sister chromatids?(each containing one DNA molecule) that are joined together at the?centromere
• The two centrosomes (replicated in the G2?phase just before prophase) move towards?opposite poles?(opposite ends of the nucleus)
• Spindle fibres?(protein?microtubules) begin to emerge from the?centrosomes?(consists of two centrioles in animal cells)
• The?nuclear envelope?(nuclear membrane)?breaks down?into small vesicles
• The nucleolus disappears

Prophase

Metaphase

• Centrosomes?reach?opposite poles
• Spindle fibres?(protein microtubules) continue to?extend from centrosomes
• Chromosomes?line up at the equator?of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosome poles
• Spindle fibres (protein microtubules) reach the chromosomes and?attach to the centromeres
  • This attachment involves specific proteins called?kinetochores

   

• Each?sister chromatid?is attached to a spindle fibre originating from?opposite poles

Metaphase

Anaphase

• The sister chromatids?separate at the centromere?(the centromere divides in two)
• Spindle fibres (protein microtubules) begin to?shorten
• The separated sister chromatids (now called chromosomes) are?pulled to opposite poles?by the spindle fibres (protein microtubules)

Anaphase

Telophase

• Chromosomes arrive at opposite poles and begin to?decondense
• Nuclear envelopes?(nuclear membranes) begin to?reform?around each set of chromosomes
• The?spindle fibres break down
• New?nucleoli form?within each nucleus

Telophase