Question

The replicated chromosomes (DNA) are then distributing to daughter nuclei by a complex series of events during cell division.

Answer 1

Hint: M phase or mitotic phase is the stage during which actual cell division occurs. It is the most complex period of the cell cycle. Before this stage, the cell duplicates its components and during this phase, the distribution of the already duplicated components occurs in an orderly manner. It consists of two processes. (i) Karyokinesis - where the division of nucleus occurs (ii) Cytokinesis - where the division of cytoplasm occurs.

Complete answer: Mitosis is a process in which the parent cells gets split into two identical daughter cells. These cells are identical in that is have the same character as each other as well as to the parent cell. It is a type of division in which already duplicated chromosomes are distributed into two daughter cells equally so that both the cells have the same number of chromosomes. Mitosis is called equational division because the two daughter cells have the same number of chromosomes as that present in the parent cell. Mitosis was first observed by Strasburger in plant cells and by Walter Flemming in the animal cells. The term mitosis was given by Walter Flemming in 1882.
It usually occurs in four stages:
1. Prophase: Pro usually means first and phase means stage, so prophase is defined as the first stage of mitosis which follows the interphase phase of the cell cycle. The following events occur during the prophase
i. The condensation of chromatin material occurs in this stage and during condensation, the DNA strands untangled that is acquired simple structure to form compact mitotic chromosomes.
ii. Each chromosome now visible as double and is made up of two coiled sister chromatids joined by a centromere. Their ends are not visible in the early prophase. Therefore, the chromosomes are visible like a ball of wool.
2. Metaphase: Meta usually means second and phase means stage, hence metaphase is the second stage of mitosis. The chromosomes now possess two chromatids attached to each other through the centromere. Mitotic spindle formation is complete. All the chromosomes align themselves at the equator.
3. Anaphase: Ana usually means up and phase means stage. Anaphase is defined as the stage where chromatids move towards the pole. Following events occur during anaphase:
i. The centromere which possesseses the two chromatids together now get divided and separated daughter chromatids are now referred to as chromosomes of the future daughter nuclei.
ii. The spindle fibres attached to the kinetochore that is to disc-like structure now shorten and daughter chromosomes begin to migrate towards the opposite poles
4. Telophase: Telo means end and phase means stage, hence, telophase is the end stage of mitosis. The following events occur during telophase
i. The chromosomes (sister chromatids) reach their respective poles. The mitotic spindle disappears.
ii. After reaching the poles, the chromosomes gradually uncoil and become thin, slender, long, and lose their identity. The decondensation of chromosomes occurs and finally, they become indistinguishable mass and collect at the poles.
iii. The nucleolus, endoplasmic reticulum, Golgi bodies, and other organelles reappear in the daughter cells.

Note: Mitosis is necessary for the growth and better development of multicellular organisms. A fertilized egg develops into an embryo which finally forms an adult by repeated mitotic divisions. Somatic cells of an organism are formed by mitosis. Mitosis maintains the size of the cell. The somatic cell that is grown more than its desired limit is induced to divide so that it maintains a proper surface area to volume ratio, which is essential for the proper functioning of the cell.