Question

In metaphase of mitosis, the chromosomes
a. Break and disintegrate
b. Undergo condensation
c. Line up at equator
d. Decondense and elongate

Answer 1

Hint: Mitosis term was given by Flemming. It is the actual phase of cell division which takes about 4% time of the complete cell cycle. It is also called equational division as it results in the formation of two daughter cells with the same number of chromosomes as in the mother cell.

Complete answer:
Mitosis includes karyokinesis i.e. nuclear division and cytokinesis i.e. cytoplasmic division.
The main phases of this cycle are- Prophase, metaphase, anaphase and telophase. Cytokinesis occurs simultaneously with anaphase or telophase or it can occur at a later stage.

• Prophase- This phase is indicated by the appearance of the chromosome as thin threads inside the nucleus. Chromosomes start to condense and it occurs by the process of folding of the chromatin fibres.
• Metaphase- It is marked by the appearance of mitotic apparatus which comprises the spindle and asters that surround the centrioles. The spindle is made of the chromosomal fibres, the continuous fibres and the interzonal fibres. After the spindle fibres invade the central area, and their microtubules extend between the poles the chromosomes become attached by the kinetochores to some of the spindle fibres and oscillate until they become radially oriented in the equatorial plane and form the equatorial plate.
• Anaphase- At anaphase the equilibrium of the forces that characterize metaphase is broken by the separation of the kinetochores. This process is carried out simultaneously in all the chromosomes. The kinetochores move apart and chromatids separate and begin their migration towards the pole.
• Telophase- The end of the polar migration of the daughter chromosomes mars the beginning of telophase. The chromosomes decondense and the nucleoli reappear at the sites of the nuclear reorganizes at this stage.

So chromosomes break up and separate in anaphase, undergo condensation in prophase, line up at equator in metaphase and decondense and elongate at telophase.

Hence, the correct answer is option (C).

Note: Mitosis is important for growth and multiplication of cells. It plays a significant role in wound healing, regeneration of damaged parts and replacement of cells lost during normal wear and tear.