POLYTENE CHROMOSOMES

1. First seen by Balbiani in salivary glands of larva of Chironomus insect (belongs to order Diptera). Later on such chromosomes observed in several other insects (Drosophila).
2. Polytene name proposed by Koller.
3. Polytene Chromosomes composed of many Chromonema (512 to several thousands).
4. In stained preparation, polytene Chromosomes appear striped with alternate dark and light bands. Dark band have high amount of histone.
5. Several puffy and swollen areas are seen on polytene Chromosomes. These called Balbiani rings or puffs.
6. Balbiani rings are site of rapid. m-RNA synthesis.
7. Ecdyson hormone (moulting hormone) of insects stimulates formation of balbiani rings.
8. Polytene chromosomes concerned with metamorphosis in insects.