What do you mean by polytene chromosome? Where are such chromosomes found?

Polytene chromosome:

1. Polytene chromosome means many threaded chromosomes.
2. In the salivary glands, Malpighian tubules and gut epithelial cells of certain insect larvae (e.g., Drosophila, Chironomus), the cell division is arrested by chromosomes that go on dividing. Hence, a single chromosome contains thousands of repeated chromatids.
3. These chromosomes are much larger in size (more than 200 times) as compared to the normal chromosome and are called polytene chromosomes (giant chromosomes).