Cleavage in the fertilized egg of humans :

Options

A. Starts in uterus
B. is meroblastic
C. starts when egg is in fallopian tube
D. is discoidal

Answer

**Step-by-Step Solution:**

1. **Understanding Cleavage**: Cleavage is the process of rapid cell division that occurs after fertilization, leading to the formation of a multicellular structure from a single-celled zygote.

2. **Formation of Zygote**: When a sperm fertilizes an egg, a zygote is formed. This zygote undergoes cleavage, which involves a series of mitotic divisions.

3. **Location of Cleavage**: In humans, cleavage begins in the fallopian tube, specifically in the ampulla region, where fertilization occurs.

4. **Stages of Cleavage**: The cleavage process leads to the formation of multiple cells, progressing through stages such as 2 cells, 4 cells, 8 cells, 16 cells, and so on. This is an exponential growth pattern.

5. **Types of Cleavage**: The question mentions terms like "meroblastic" and "discoidal."
- **Meroblastic Cleavage**: This type of cleavage occurs in species with a significant amount of yolk in the egg (like amphibians and birds) and is not applicable to humans.
- **Discoidal Cleavage**: This type is also related to species with a lot of yolk and is not relevant to human development.

6. **Conclusion**: The correct answer to the question is that cleavage starts when the egg is in the fallopian tube, as this is where the zygote forms and begins its rapid division.

**Final Answer**: Cleavage in the fertilized egg of humans starts when the egg is in the fallopian tube.

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