Question

In synthesis(S) phase of the cell cycle,

• A. the amount of DNA doubles and chromosome number increases
• B. the amount of DNA and chromosome number remains constant
• C. the amount of DNA doubles and chromosome number remains constant
• D. the amount of DNA is reduced to half and chromosome number decreases

Answer 1

The correct option is C the amount of DNA doubles and chromosome number remains constant

Cell cycle includes an orderly sequence of events during which cell synthesises cellular contents, duplicates its genome and eventually divides forming daughter cells. Cell cycle includes two phases - interphase and mitotic phase.

Interphase is a non dividing phase during which cell prepares to divide. Interphase includes G${}_1$, S and G${}_2$ phases.

During S phase (synthesis phase), DNA undergoes replication and makes a copy of itself. Hence, the content of DNA doubles during S phase. Each chromosome after DNA replication will have two chromatids and there is no change in the chromosome number. Hence, the chromosome number remains constant during S phase.