Question

Why chromosome number doesn't increase in S phase eventhough DNA gets doubled?

Answer 1

During the S phase or synthesis phase, the DNA synthesises or replicates, and the amount of DNA in the cell doubles without any increase in the number of chromosomes. Also, the centriole begins to duplicate in the cytoplasm.

During S phase, chromosomes replicate to give rise to two identical sister chromatids. These sister chromatids remain attached at their kinetochores. Hence there is no increase in number of chromosomes during S phase even though DNA replicates to increase its amount.