In oogenesis, haploid egg is fertilized by sperm at which stage?

Options

A. Ovum
B. Oogonium
C. Primary oocyte
D. Secondary oocyte

Answer

**Step-by-Step Solution:**

1. **Understanding Oogenesis**: Oogenesis is the process of egg (ovum) development in females. It begins with the formation of oogonia, which are the immature egg cells.

2. **Formation of Primary Oocytes**: Oogonia undergo mitosis to form primary oocytes. These primary oocytes are diploid (2n) and are arrested in prophase I of meiosis until puberty.

3. **Meiosis I**: Upon reaching puberty, primary oocytes resume meiosis and complete meiosis I, resulting in the formation of a secondary oocyte and a first polar body. Both of these cells are haploid (n).

4. **Meiosis II**: The secondary oocyte then enters meiosis II but is arrested at metaphase II. It will only complete meiosis II if fertilization occurs.

5. **Fertilization**: The haploid egg (secondary oocyte) is fertilized by a sperm cell at the metaphase II stage of meiosis. If fertilization occurs, the secondary oocyte completes meiosis II, resulting in the formation of the ovum and another polar body.

6. **Conclusion**: Therefore, the haploid egg is fertilized by sperm at the stage of the secondary oocyte.

**Final Answer**: The haploid egg is fertilized by sperm at the stage of the secondary oocyte.

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