Explanation
Cytokinesis is the final process in eukaryotic cell division, which divides the cytoplasm, organelles, and cellular membrane to give rise to daughter cells. In most animals, cytokinesis begins sometime in late anaphase or early telophase, to ensure the chromosomes have been completely segregated. The movements of cytokinesis seen in the cell are caused by the same spindle network that was responsible for the separation of the chromosomes.
In animal cells, after sister chromosomes have separated, the remaining non-kinetochore, overlapping microtubules form a structure called the spindle midzone. At this time, the actomyosin ring begins to assemble and contract. The remaining of the spindle midzone persists as a structure known as the residual body or midbody that has been compressed by the ingressing cleavage furrow. The midbody is a compact, dense matrix of proteins present in the region of microtubule overlap that is formed from the spindle midzone and cleavage furrow. It fills the intercellular channel connecting daughter cells at the completion of cytokinesis in animal cells and is a narrow structure with a typical diameter of 1 micrometer and a length of 3 to 5 micrometers. Hence, option A is correct.
Meiosis is a special type of cell division, a process where a single cell divides two times to produce four haploid cells, each not only containing half the original amount of genetic information but also genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes including animals, plants and fungi. Meiosis produces our sex cells or gametes (eggs in females and sperm in males, both haploid cells). When a sperm and an egg join in fertilization, the two haploid sets of chromosomes form a complete diploid set which gives rise to a new genome. Therefore, in meiosis, a diploid cell (2n; one that has two sets of chromosomes), becomes a haploid cell (n; one that has one set of chromosomes). Therefore, it is a very important process because errors in this result in aneuploidy, developmental disabilities etc. The correct answer is option C.
Karyokinesis is division of the nucleus during cell cycle. It is the first step during the mitosis or meiosis of the cell cycle and results in the formation of two daughter nuclei which corresponds to separation of daughter chromosomes into these two nuclei. It is generally followed by cytokinesis which is nothing but the division of the cytoplasm to form two separate daughter cells immediately after mitosis. It results in separation of organelles, including the nuclei, into the two daughter cells. Karyokinesis is independent of cytokinesis; it can occur without being followed by cytokinesis. Cytokinesis cannot take place without karyokinesis i.e. it is dependent on karyokinesis. The correct answer is B.
Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase. These phases occur in this strict sequential order, and cytokinesis - the process of dividing the cell contents to make two new cells - starts in anaphase or telophase.
1. Prophase - During prophase, chromosomes get visible (chromatids), the centrioles migrate to the poles, nuclear membrane and nucleolus disappear and spindle formation is seen. Prophase in mitosis is longer than any other phases of mitosis because the cell has to prepare for the actual division that takes place from early through late prophase.
2. Metaphase - During this, chromosomes lineup around the centre (Cells in metaphase have the chromosomes, which appear as long thin strands under the microscope).
3. Anaphase - here, chromatids separate and move to opposite poles by spindle fibers. This allows each daughter cell to have an identical copy of each of the original cell’s chromosomes.
4.Telophase - During this phase, chromosomes disappear (become chromatin), nuclear membrane reforms, nucleoli reappears, spindle disappears and centrioles duplicate.
The correct answer is option B.
Please disable the adBlock and continue. Thank you.
