In metagenesis of cnidarian like Obelia, the polyps and medusae are respectively

Options

A. N and 2N
B. 2N and N
C. 2N and 2N
D. N and N.

Answer

**Step-by-Step Solution:**

1. **Understanding Metagenesis**: Metagenesis refers to the alternation of generations between sexual and asexual reproduction. In the case of cnidarians like Obelia, this involves a cycle between two forms: polyps and medusae.

**Hint**: Remember that metagenesis involves both asexual and sexual reproduction.

2. **Identifying Cnidarians**: Cnidarians are a phylum of animals that include organisms such as jellyfish, corals, and sea anemones. Obelia is a specific genus within this phylum.

**Hint**: Cnidarians are known for their two body forms: polyp and medusa.

3. **Defining Polyps and Medusae**: Polyps are the sessile (attached) form of cnidarians, while medusae are the free-swimming form. Polyps reproduce asexually, typically through budding, while medusae reproduce sexually.

**Hint**: Think of polyps as the stationary stage and medusae as the mobile stage.

4. **Reproduction Process**: In Obelia, polyps reproduce asexually to form medusae. This process does not involve gametes, so the chromosome number remains the same. When medusae reproduce, they do so sexually, producing gametes that are haploid (n).

**Hint**: Asexual reproduction maintains the chromosome number, while sexual reproduction results in haploid gametes.

5. **Chromosome Number**: If we assume the diploid number of chromosomes in the polyp is 2n (for example, 10), then the medusa, which arises from the polyp asexually, will also have the same diploid number (2n = 10). However, when medusae reproduce sexually, they produce haploid gametes (n = 5).

**Hint**: Remember that diploid (2n) means two sets of chromosomes, while haploid (n) means one set.

6. **Conclusion**: Therefore, in the metagenesis of Obelia, the polyps are diploid (2n) and the medusae are also diploid (2n) when formed asexually. However, during sexual reproduction, the gametes produced by medusae are haploid (n).

**Final Answer**: In metagenesis of cnidarians like Obelia, the polyps are diploid (2n) and the medusae are also diploid (2n) when formed asexually.

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