Which of the following does not occur during mitosis?

a. condensation of the chromosomes

b. replication of the DNA

c. separation of sister chromatids

d. spindle formation

Option (b).

Explanation:

Mitosis may be defined as the process of cell division in which a single parent cell divides into two cells. This division is known as reduction division because the chromosome number remains the same.

The chromosome condensation, spindle formation and sister chromatid separation occurs in mitosis. The replication of DNA occurs in the synthesis phase of cell cycle not during the process of mitosis.

Thus, the correct answer is option (b).