Describe an example of a fossil that consists of an entire organism
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Answer:
Mitosis is a type of cell division in which single haploid cell (n) or diploid cell (2n) divides into two haploid or diploid daughter cells that are same as the parent.
Mitosis occurs in somatic cells of plants and animals. In this cell division, the two daughter cells have the same number of chromosomes as that in the parent cells.
Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase.
1.Prophase:-
It is the first visible stage in karyokinesis. The chromosomes appear as long coiled threads called chromatids. The chromatin becomes shorter, thicker and visible due to the condensation of DNA. The chromatins are now called chromosomes. Stainability of nucleus increase. Each chromosome starts to splits longitudinally into two sister chromatids. These sister chromatids are attached to each other at the centromere. The nuclear membrane and nucleolus start to disappear and by the end, it will be completely disappeared.
ii. Metaphase:-
Nuclear membrane and nucleolus completely disappears and simultaneously appearance of spindle fibers. Spindle fibers are attached to the centromere of a chromosome. The chromosomes are arranged on the equatorial plane. The process of gathering of chromosomes in equator is called congressional and plate formed is called metaphasic plate.
iii. Anaphase:-
The centromere of each chromosome splits into two sister chromatids and forms two daughter chromosomes. The daughter chromosomes are pulled towards the poles due to the contraction of spindle fibres and stretching of interzonal fibers. During polar movement, the chromosomes show different shapes i.e. J, U, V, L or I shaped in appearance. At the end of anaphase, each pole will get one set of daughter chromosomes. It is the shortest phase and is also known as a migratory phase.
iv. Telophase:- The daughter chromosomes reach respective poles and uncoil and become thin, long and visible. The spindle fibres start disappearing and finally disappear. The nuclear membrane and the nucleolus reappear.
Two nuclei are formed at the end of telophase. Both the nuclei have the same number of chromosome as the parent cell. It is the last visible stage of karyokinetic and is also known as reorganization phase.
It is followed by cytokines or division of cytoplasm.
Explanation:
