A swelling in the band of a polytene chromosome is an indication of :-

Options

A. Gene action
B. Gene inaction
C. Mutation
D. Gene damage

Answer

**Step-by-Step Solution:**

1. **Understanding Polytene Chromosomes:**
- Polytene chromosomes are large chromosomes formed from specialized cells that undergo multiple rounds of DNA replication without cell division. This results in a structure with many copies of each gene.

2. **Identifying the Swelling:**
- The swelling observed in the bands of polytene chromosomes is indicative of regions of active gene expression. These swellings are known as "puffs."

3. **Analyzing the Options:**
- **Option 1: Gene action** - This option is correct because the swellings (or puffs) represent areas where genes are actively being transcribed and expressed.
- **Option 2: Gene inaction** - This option is incorrect as swelling indicates active gene expression, not inactivity.
- **Option 3: Mutation** - This option is also incorrect; mutations do not directly cause swelling in polytene chromosomes.
- **Option 4: Gene damage** - This option is incorrect as swelling does not indicate damage but rather active gene function.

4. **Conclusion:**
- The swelling in the band of a polytene chromosome is an indication of gene action, making **Option 1** the correct answer.