Question

The nucleus of a diploid organism contains 3 ng of DNA in $G_1$-phase. Which one of the following statements describes the state of the cell at the end of S-phase?

• A. The nucleus divides into two and each nucleus contains 3 ng of DNA
• B. The nucleus does not divide and it contains 3 ng of DNA
• C. The nucleus divides into two and each nucleus contains 1.5 ng of DNA
• D. The nucleus does not divide and it contains 6 ng of DNA

Answer 1

Answer: (D)

In the $G_2$ -phase of cell cycle, the cell grows in size, i.e. the cell synthesises various enzymes and nutrients that are needed later on for DNA replication. The next phase of cell cycle is S-phase during which the DNA amount doubles up, i.e. a cell with 3 ng of DNA in $G_1$ -phase will now have 6 ng of DNA. $G_2$-phase comes after S-phase. It is second growth phase but here the DNA content will remain 6 ng.