They are also known as polytene chromosomes. They commonly occur in the dipteran species of the flies such as Drosophila. First, they look like normal chromosomes. However, later on, these regions undergo repeated rounds of DNA replication. They look longer than the normal chromosomes. Hence, they are known as the giant chromosomes. The process of repeated DNA replication without the cell division is known as endoreplication. However, the centromere does not undergo endoreplication. The reason remains unclear. The process of replication requires the removal of the internal eliminated sequences (IES). The non-coding genes get removed or excised. The polytene chromosomes become larger and appear banded. A rare event occurs in the cells with the polytene chromosome. The centromeres come together and bundle up. The structure so formed is known as a chromocenter. Dissecting the Drosophila larvae and observing their cells under the microscope reveals polytene chromosomes. They commonly occur in the larvae as compared with the adult flies. Balbiani first reported these chromosomes in the year 1881. Thousands of DNA strands occupy the polytene chromosomes. They play a crucial role in the salivary glands. A polytene band represents the vertical stripes on the polytene chromosomes. It results from the specified association between the homologous chromomeres. A somatically paired bundle of chromosomes consists of these chromomeres at the same level. The polytene chromosome is also known as the Balbianin chromosome due to the presence of large puffs known as Balbiani rings. The RNA puffs rarely exist.