Question

If a cell with 5 chromosome pairs undergoes mitosis, then what is the total number of chromosomes in its anaphase stage?
A. 5
B. 10
C. 15
D. 20

Answer 1

Hint: In eukaryotes, two types of cell division occurs i.e. Mitosis and meiosis. In mitosis, the parent cell divides into two daughter cells and each receives an exact copy of the chromosome in the parent cell. In Meiosis, the genetic material in the daughter cell is reduced to half that of the parental chromosome number so that fertilization will restore the diploid complement.

Complete answer: The cell cycle is an ordered series of events. The mitotic phase starts with karyokinesis and this results in the formation of daughter nuclei. The mitotic phase ends with cytokinesis. Mitosis is conventionally divided into 4 phases. They are Prophase, Metaphase, Anaphase, and Telophase. In prophase, ‘pro’ stands for before. Diffuse chromatin begins to condense in this phase. Chromatin condensed into a well-defined chromosome. Each chromosome is already replicated in the S phase of the cell cycle. In metaphase, ‘meta’ stands for the middle. Metaphase is an extremely dynamic phase of the cell cycle. Spindle fibers rapidly assemble and disassemble. Chromosomes get attached to spindle fiber via kinetochore. Chromosomes are attached at the equator of the cell. In anaphase, ‘ana’ stands for the back. In anaphase chromosome splits at the centromere. Centromere divides and the two sister chromatids. Chromatids move towards opposite poles. The movement of chromatids is carried out by spindle fibers. If the cell has 5 chromosomes, during the S phase it replicates. So, the number of chromosomes entering mitosis will be 10 chromosomes. During anaphase chromosomes split into chromatids. Each chromatid acts as a chromosome and migrates towards the opposite pole. So, the cell initially with 5 chromosomes has 20 chromosomes during anaphase.
So, the correct answer to the given question is option D, i.e., 20.

Note: Meiosis is called a reductional division and mitosis is called an equational division. Mitotic division occurs in the somatic cell and hence called somatic cell division. Meiosis occurs in germ cells that produce gametes. In meiosis haploid state is attained to maintain the ploidy of the organism at the time of fertilization.