What is not true about cell cycle ?
a. During `G_(1)` phase there is active synthesis of RNA and proteins but no change in its DNA content
b. In synthesis or S phases, each chromosome carriers a duplicate set of genes
c. During `G_(2)` phase, a cell contains double the amount (C) of DNA present in the original diploid cell (2n)
d. In S-phase a cell doubles the original diploid (2n) chromosome number

Options

A. c & d
B. b & c
C. d only
D. b, c & d

Answer

To determine which statement is not true about the cell cycle, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Statement A:** "During G1 phase there is active synthesis of RNA and proteins but no change in its DNA content."
- **Analysis:** This statement is true. During the G1 phase, the cell is actively synthesizing RNA and proteins to prepare for DNA replication, but the DNA content remains unchanged as replication occurs only in the S phase.

2. **Statement B:** "In synthesis or S phase, each chromosome carries a duplicate set of genes."
- **Analysis:** This statement is also true. During the S phase, DNA replication occurs, resulting in each chromosome having a duplicate set of genes. The chromatin (which is the form of DNA during interphase) is duplicated, leading to two identical sister chromatids for each chromosome.

3. **Statement C:** "During G2 phase, a cell contains double the amount (C) of DNA present in the original diploid cell (2n)."
- **Analysis:** This statement is true. By the end of the S phase, the DNA content has doubled, and during the G2 phase, the cell contains double the amount of DNA (4n) compared to the original diploid state (2n).

4. **Statement D:** "In S-phase a cell doubles the original diploid (2n) chromosome number."
- **Analysis:** This statement is false. During the S phase, the chromosome number does not change; instead, the amount of DNA doubles. The chromosome number remains the same until the cell undergoes mitosis or meiosis, where the centromeres split, leading to the separation of sister chromatids.

### Conclusion:
The statement that is not true about the cell cycle is **Statement D**.

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