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 times the number of chromosomes and twice the amount of DNA
D. twice the number of chromosomes and twice the amount of DNA

Answer

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**:
- A somatic cell is a body cell that is typically diploid, meaning it contains two sets of chromosomes (one from each parent).
- A gamete is a reproductive cell (sperm or egg) that is haploid, meaning it contains only one set of chromosomes.

2. **Identify the S-phase**:
- The S-phase (Synthesis phase) of the cell cycle is when DNA replication occurs. This means that the amount of DNA in the cell doubles as each chromosome is replicated.

3. **Determine the Chromosome Count**:
- Since a somatic cell is diploid, it has 2n chromosomes. After completing the S-phase, it will still have 2n chromosomes, but each chromosome will consist of two sister chromatids.
- A gamete, being haploid, has n chromosomes.

4. **Determine the Amount of DNA**:
- Before the S-phase, the somatic cell has a certain amount of DNA. After the S-phase, the amount of DNA doubles because each chromosome has been replicated.
- Therefore, the somatic cell will have 4 times the amount of DNA compared to the original amount (2n chromosomes with 2 copies each = 4n total DNA).

5. **Comparison**:
- Now, comparing the somatic cell (after S-phase) with the gamete:
- The somatic cell has twice the number of chromosomes (2n vs n).
- The somatic cell has four times the amount of DNA (4n vs n).

6. **Conclusion**:
- The correct answer is that the somatic cell has twice the number of chromosomes and four times the amount of DNA compared to the gamete.

### Final Answer:
The correct option is **B: twice the number of chromosomes and four times the amount of DNA**.