During embryonic development of human, second cleavage is completed after about

Options

A. 30 hours of fertilization
B. 60 hours of fertilization
C. 72 hours of fertilization
D. 48 hours of fertilization

Answer

**Step-by-Step Solution:**

1. **Understanding Cleavage**: Cleavage refers to the series of rapid cell divisions that occur after fertilization, leading to the formation of a multicellular embryo. It is characterized by the division of the zygote into smaller cells called blastomeres.

2. **First Cleavage**: The first cleavage occurs shortly after fertilization, resulting in the formation of two cells from the original zygote. This is known as the 2-cell stage.

3. **Second Cleavage**: Following the first cleavage, the second cleavage occurs. This division results in the formation of four cells, leading to the 4-cell stage.

4. **Completion of Second Cleavage**: The second cleavage further divides the four cells into eight cells, resulting in the 8-cell stage. This stage is referred to as the blastomere stage.

5. **Time Frame**: The second cleavage is completed approximately 60 hours after fertilization. This is a crucial point in embryonic development as it marks the transition from the 4-cell stage to the 8-cell stage.

6. **Conclusion**: Therefore, during embryonic development in humans, the second cleavage is completed after about 60 hours post-fertilization.

**Final Answer**: The second cleavage is completed after about 60 hours.

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