Question

How many chromosomes shall be present in a diploid cell at mitotic anaphase, if its egg cell has ten chromosomes?
a. 10
b. 20
c. 30
d. 40

Answer 1

Hint: Mitosis, also known as equational division, is a process by which a cell divides to form two identical daughter cells. Mitosis mainly occurs in regions that are undergoing growth or replacing worn-out tissues. Also, anaphase is the stage of mitosis in which the sister chromatids are pulled to the opposite poles. Even though the chromatids are at opposite ends, they are still bound by a single cell membrane.

Complete answer:
If the egg cell has ten chromosomes, the number of chromosomes present at the mitotic anaphase stage would be twenty. As mentioned, mitosis is also known as equational division. This means that the number of chromosomes in each daughter cell is the same as the number of chromosomes in the parent cell. In order to accomplish this, the nuclear content (chromosomes) duplicates, and two sets of chromosomes are formed. This happens during the Interphase of mitosis. During anaphase, each sister chromatid is pulled towards the opposite poles by mitotic spindles.

Now, when we correlate this with the given case, we can understand the following:
- In interphase, the number of chromosomes in the egg cell duplicate and form 20 chromosomes, i.e. 2 sets of chromosomes.
- During anaphase, when the sister chromatids are pulled, each pole would contain half of the nuclear matter, i.e. 10 chromosomes.
- Even though each pole contains 10 chromosomes, the cell has not yet divided and is still surrounded by a single cellular membrane.
- This means that at anaphase, there are 20 chromosomes in the egg cell.

Hence, the correct answer is option (B).

Note: At the end of the anaphase, the nuclear envelope starts forming around the chromosomes at the opposite poles. This results in the formation of two nuclei. Also, the cell starts pinching inwards to divide into two cells, thus creating two new daughter cells, each having a full set of chromosomes (10 each). This phase is referred to as telophase.