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

To solve the question regarding the timing of the second cleavage during human embryonic development, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Cleavage**: Cleavage refers to the series of rapid mitotic divisions that the zygote undergoes after fertilization. This process transforms the single-celled zygote into a multicellular structure.

2. **First Cleavage**: The first cleavage occurs approximately 24 hours after fertilization. This division results in the formation of two cells from the original zygote.

3. **Second Cleavage**: Following the first cleavage, the second cleavage occurs. This is the division of the two cells formed during the first cleavage, resulting in a total of four cells.

4. **Timing of Cleavages**: Each cleavage division in the zygote takes about 24 hours to complete. Therefore, the second cleavage will occur 24 hours after the first cleavage.

5. **Calculating Time**: Since the first cleavage occurs at about 24 hours post-fertilization, the second cleavage will be completed at approximately 24 hours + 24 hours = 48 hours after fertilization.

6. **Conclusion**: Thus, the second cleavage is completed after about 48 hours.

### Final Answer:
The second cleavage during human embryonic development is completed after **48 hours**.

---