In animal cells, during the S-phase -

Options

A. DNA replication occurs in nucleus and centrioles duplicate in the cytoplasm
B. Only DNA replication occurs in nucleus
C. Only Centrioles duplicate in the cytoplasm
D. Centrioles duplicate in the nucleus and DNA replication occurs in the cytoplasm.

Answer

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**:
- The cell cycle consists of several phases, including interphase (which has G1, S, and G2 phases) and mitosis. The S-phase is specifically known as the synthesis phase.

2. **Identifying the S-phase**:
- The S-phase is crucial because it is the period during which DNA replication occurs. This means that the genetic material of the cell is duplicated in preparation for cell division.

3. **DNA Replication**:
- During the S-phase, DNA replication takes place in the nucleus. This involves unwinding the DNA double helix and synthesizing new strands complementary to the original strands.

4. **Centrioles Duplication**:
- In addition to DNA replication, centrioles, which are structures involved in cell division, also duplicate during the S-phase. Centrioles are located in the cytoplasm, and their duplication is essential for proper cell division.

5. **Summary of Events**:
- In summary, during the S-phase in animal cells, both DNA and centrioles are duplicated. DNA replication occurs in the nucleus, while centrioles duplicate in the cytoplasm.

### Final Answer:
In animal cells during the S-phase, DNA replication occurs in the nucleus, and centrioles duplicate in the cytoplasm.

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