Cell Cycle and Cell Division Test - 46

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.