During which phase(s) of cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C?

The correct answer is option 'A'. Only G2 phase of the cell cycle maintains the DNA content at 4C level if the initial amount is denoted as 2C.

Explanation:

The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells. It consists of several phases, including G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis).

- G1 Phase: This is the first phase of the cell cycle, during which the cell grows and carries out its normal functions. The DNA content in the cell is denoted as 2C.

- S Phase: In this phase, DNA replication occurs. Each chromosome is duplicated, resulting in the formation of sister chromatids. The DNA content in the cell doubles, becoming 4C.

- G2 Phase: This is the second gap phase, during which the cell continues to grow and prepares for cell division. The DNA content in the cell remains at 4C.

- M Phase: This phase involves the actual division of the cell into two daughter cells through processes such as mitosis and cytokinesis. The DNA content in each daughter cell is reduced back to 2C.

Explanation of the correct answer:

The amount of DNA in a cell remains at 4C level during the G2 phase of the cell cycle. This is because DNA replication occurs in the S phase and the DNA content doubles from 2C to 4C. The G2 phase follows the S phase and precedes the M phase. During the G2 phase, the cell undergoes further growth and prepares for cell division. The DNA content remains at 4C during this phase as it has already been replicated in the S phase.

The other phases mentioned in the options do not maintain the DNA content at 4C.
- G0 phase is a non-dividing state where cells are not actively preparing for cell division.
- G1 phase is the phase before DNA replication occurs, so the DNA content is still at 2C.
- S phase is when DNA replication occurs, resulting in the doubling of DNA content to 4C.
- M phase is when cell division takes place, and the DNA content is reduced back to 2C in each daughter cell.

Therefore, the correct answer is option 'A'. Only the G2 phase of the cell cycle maintains the DNA content at 4C level if the initial amount is denoted as 2C.