Third phase of embryo development is

Options

A. Cleavage
B. Fertilization
C. Gametogenesis
D. Gastrulation.

Answer

**Step-by-Step Text Solution:**

1. **Understanding Embryo Development Phases**: The development of an embryo occurs in several distinct phases, each with specific processes that contribute to the formation of a fully developed organism.

2. **Identifying the Phases**: The main phases of embryo development include:
- **Fertilization**: The fusion of male and female gametes to form a zygote.
- **Cleavage**: The rapid mitotic divisions of the zygote, leading to the formation of a morula.
- **Gastrulation**: The process where the blastocyst transforms into a gastrula, leading to the formation of three germ layers.

3. **Determining the Third Phase**:
- The first phase is **Fertilization**.
- The second phase is **Cleavage**.
- The third phase is **Gastrulation**, which begins around the third week of development.

4. **Conclusion**: The third phase of embryo development is **Gastrulation**.

**Final Answer**: Option D: Gastrulation.

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