During the fourth and sixth cleavage of the zygote

Options

A. Mesomeres give rise to endoderm
B. Micromeres give rise to ectoderm
C. Mesomeres give rise to mesoderm
D. Macromeres give rise to ectoderm

Explanation

**Step-by-Step Solution:**

1. **Understanding Cleavage**: After fertilization, the zygote undergoes a series of rapid mitotic divisions known as cleavage. This process results in the formation of smaller cells called blastomeres.

2. **Identifying Cleavage Stages**: The question specifically asks about the 4th and 6th cleavages of the zygote. During these stages, the zygote continues to divide, leading to the formation of different types of blastomeres.

3. **Types of Blastomeres**:
- **Micromeres**: These are smaller cells that arise during cleavage and are associated with the formation of the ectoderm.
- **Macromeres**: These are larger cells that can give rise to the mesoderm and endoderm.

4. **Germ Layer Formation**:
- During the 4th cleavage, micromeres contribute to the formation of the ectoderm.
- During the 6th cleavage, the micromeres continue to play a role in the development of the ectoderm, while macromeres contribute to the mesoderm and endoderm.

5. **Conclusion**: Therefore, during the 4th and 6th cleavages, the micromeres are primarily responsible for the formation of the ectoderm, while the macromeres contribute to the formation of the mesoderm and endoderm.

**Final Answer**: During the 4th and 6th cleavage of the zygote, micromeres give rise to the ectoderm.

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