Question

32. Explain Prophase and Metaphase stages of Mitosis division.​

Answer 1

Mitosis is a type of cell division where a single cell divides to produce two genetically identical daughter cells.

Prophase stage:

• The process of mitosis begins with prophase.
• In this stage, chromosomes shorten and thicken and migrate towards the cell center.
• During this stage, the nuclear envelope breaks down and spindles form at opposite poles of the cell.

Metaphase stage:

• Metaphase is the second stage of mitosis division.
• In this stage, chromosomes get lined up at the equator (metaphase line) before being split apart for each of the two daughter cells.
• During this stage, the nuclear membrane disappears completely.

Answer 2

Answer:

Mitosis refers to the equational division as it results in two daughter cell divisions having an equal number of chromosomes as the parent cell.

Mitosis is also called somatic cell division.                

Explanation:

• In a somatic cell, the mitotic cycle includes two parts- Interphase and mitosis.

• The mitotic phase or M phase includes Karyokinesis and cytokinesis.

• And further, it includes 4 stages of Karyokinesis namely- Prophase, Metaphase, anaphase and telophase.

1. Prophase: The longest phase/Stage of the Mitotic Phase:

• It involves several changes in the cell which take place more or less simultaneously.

• A new set of two centrioles appears de novo. The two sets of paired centrioles move apart and migrate towards the opposite poles of the cell.

• Numerous fine protoplasmic fibres (microtubules) appear around each centriole, radiating from it like the rays of a star. They are termed asters or aster rays.

• Side by side, some important changes take place in the nucleus. The fine chromatin threads shorten and thicken by undergoing dehydration and spiral coiling.

• Their coiling is called spiralization. These threads are now known as chromosomes.

• Each chromosome has a single, clear, non-staining and rounded granule the centromere with which are attached two identical chromatids which have already been formed in the S phase. Each chromatid possesses a complete set of DNA molecules.

• Numerous fine fibres make their appearance on way to form a spindle between the two sets of paired centrioles.

• The microtubules are made up of RNA (3.5%) and a single type of protein which somewhat resembles the contractile protein actomyosin of muscle cells.

• While the above changes go on, the nucleolus and nuclear membrane gradually disappear and the nuclear material mixes with the cytoplasm.

• With these changes, the prophase comes to an end.

2. Metaphase Stage of Mitotic Phase:

• While the spindle is being formed, the chromosomes, with their chromatids still attached, move towards the equatorial plane of the cell, i.e., the plane midway between the two poles.

• During their movement, the centromeres are kept forward so that each appears to be dragging a pair of chromatids behind it.
• At the equatorial plane, each centromere gets attached to two opposing fibres of the spindle.

• The first part of metaphase after the end of the prophase is called 'prometaphase'.
• At this stage nuclear envelope dissolves and a definitive mitotic spindle is formed. Condensed chromosomes are scattered in the nuclear region.

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