A somatic cell that has just completed the S-phase of its cell cycle, as compared to gamete of the same species, has

Options

A. Same number of chromosomes but twice the amount of DNA
B. Twice the number of chromosomes and four times the amount of DNA
C. Four time the number of chromosomes and twice the amount of DNA
D. Twice the number of chromosmes and twice the amount of DNA

Explanation

To solve the question regarding the comparison between a somatic cell that has just completed the S-phase of its cell cycle and a gamete of the same species, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Cell Types**:
- Somatic cells are diploid (2n), meaning they contain two sets of chromosomes (one from each parent).
- Gametes (sperm and egg cells) are haploid (n), meaning they contain only one set of chromosomes.

2. **Identify the S-phase**:
- The S-phase (Synthesis phase) of the cell cycle is when DNA replication occurs. After the S-phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome.

3. **Determine Chromosome Count**:
- Before the S-phase, a diploid somatic cell has 2n chromosomes. After the S-phase, while the amount of DNA doubles, the number of chromosomes remains the same (2n), but each chromosome now consists of two sister chromatids.
- In contrast, a gamete has n chromosomes.

4. **Determine DNA Content**:
- Before the S-phase, the DNA content of the somatic cell is 2C (where C represents the amount of DNA in a single chromosome). After the S-phase, the DNA content doubles to 4C because each of the 2n chromosomes now has two copies (sister chromatids).
- The gamete has a DNA content of C.

5. **Comparison**:
- When comparing the somatic cell (after S-phase) to the gamete:
- The somatic cell has the same number of chromosomes (2n) as before, but now has 4 times the amount of DNA (4C).
- The gamete has n chromosomes and C amount of DNA.

6. **Conclusion**:
- Therefore, the correct answer is that the somatic cell has twice the number of chromosomes (2n compared to n) and four times the amount of DNA (4C compared to C).

### Final Answer:
A somatic cell that has just completed the S-phase of its cell cycle, as compared to a gamete of the same species, has **twice the number of chromosomes and four times the amount of DNA**.

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