Question

What are the stages of mitosis?

Answer 1

MITOTIC PHASE - At this stage of cell cycle, cell division takes place.

It consists five stages:

1. Prophase: chromosomes condensed and visible; formation of spindle fibres initiates; breakdown of nuclear membrane.
2. Prometaphase: kinetochore microtubules attached to the centromere of the chromosomes (sister chromatids) that are also known as spindle fibres.
3. Metaphase: duplicated chromosomes (sister chromatids) arranged at metaphase plate and connected with spindle fibres formed by the pair of centrioles from the poles of the cell.
4. Anaphase: with the help of spindle fibres, centromere of each pair of chromosomes migrate towards the pole of the cell i.e. migration of sister chromatids to the opposite direction to each other in the cell. Process of cytokinesis begins.
5. Telophase: chromosomes begin invisible, nuclear membrane appears and at the end of cytokinesis in late telophase two daughter cells formed.

PROPHASE:

There are two stages of prophase:

1. Early prophase:

• Replicated centrioles begin to move towards the pole of the cell
• Replicated chromosomes become condensed and visible
• Nucleolus becomes invisible (disappear)

1. Late prophase:

• Formation of spindle fibres between two centrioles
• Chromosomes are visible in the form of two sister chromatids
• Breakdown of nuclear envelope

PROMETAPHASE:

1. At the end of prophase, chromosomes become visible, duplicated centriole forms spindle outside the nucleus and nuclear membrane disappears.
2. Sometimes transitions occur between prophase and metaphase, which is generally known as prometaphase.
3. Prometaphase is a short period in which chromosomes are in disorder.

METAPHASE:

1. At the end of this short period, chromosomes arranged to the specific imaginary plane that is called as metaphase plate.
2. Arrangement of chromosomes at the metaphase plate is conducted by the spindle fibres that are connected to the centromere, which helps chromosomes to aligned perpendicular to the spindle apparatus called centrioles.
3. In this phase many fibres are connected to the centromeres called as chromosomal fibres whereas many of the fibres are extended from one pole to the other of the cell are called as continuous fibres.

ANAPHASE:

1. The main event of anaphase is chromatid separation towards the opposite poles of the cell.
2. This event occurs with the sister chromatid of metaphase which requires huge amount of energy.
3. The migration of chromatids (daughter chromosomes) continues till the reach to the end of the poles.
4. Cytokinesis initiates at the end of anaphase.

TELOPHASE:

1. The two important events of telophase is as below:
   • Formation of nuclear membrane around the set of chromatids.
   • Reappearance of nucleoli.
2. At the end of polar migration of chromosomes, telophase begins.
3. During telophase chromosomes aggregate and an envelope kind of structure form around the set of aggregated chromosomes.
4. Here the newly formed envelope is known as nuclear membrane.