CBSE Class 10 Answered

Mitosis cannot occur without the replication of DNA in S phase. Two important events take place during S phase:

1. Synthesis or duplication of DNA

2. Duplication of centriole

DNA duplication is important as it maintains the chromosome number in the daughter cells. Since mitosis is an equational division, DNA replication is an important step of mitosis.

There can be DNA replication without cell division. During cell division, the parent cell gets divided into two daughter cells. If there is repeated replication of DNA without cell division, the DNA so formed will keep accumulating inside the cell. This would increase the volume of the cell nucleus, thereby causing cell expansion.

Example: DNA replication without cell division is observed in the salivary glands of Drosophila. The chromosome undergoes repeated DNA duplication resulting in the formation of polytene chromosome.