Karyogamy is

Options

A. Fusion of two germ cells
B. Fusion of two gametic nuclei
C. Fusion of a somaic cell and a reproductive cell
D. Fusion of two somatic cells.

Answer

**Step-by-Step Solution:**

1. **Understanding the Terms:**
- The term "karyogamy" is derived from two Greek words: "karyo," meaning nucleus, and "gamy," meaning fusion.

2. **Definition of Karyogamy:**
- Karyogamy refers specifically to the fusion of two gametic nuclei. This process is a crucial step in sexual reproduction, particularly in fungi and other organisms.

3. **Differentiating from Other Processes:**
- It is important to distinguish karyogamy from other types of cell fusion:
- **Somatogamy:** This is the fusion of two somatic (body) cells, which is not what karyogamy refers to.
- **Fusion of a somatic cell and a reproductive cell:** This is not a recognized process in biological terms.
- **Fusion of two germ cells:** This is also incorrect in the context of defining karyogamy.

4. **Example in Fungi:**
- In fungi, during sexual reproduction, haploid cells undergo mitosis to form haploid gametes.
- These gametes fuse in a process called plasmogamy (fusion of cytoplasm), leading to a dikaryotic stage where two nuclei coexist in one cell.
- Eventually, these nuclei will undergo karyogamy, resulting in the formation of a diploid zygote, which will then undergo meiosis to produce haploid spores.

5. **Conclusion:**
- Based on the definitions and examples provided, the correct answer to the question "Karyogamy is" is the fusion of two gametic nuclei.

**Final Answer:**
Karyogamy is the fusion of two gametic nuclei.

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