Polytene chromosome is the largest chromosome found in the salivary gland. Therefore, this chromosome is also known as the salivary gland chromosome. The size of the polytene chromosome is up to 2000 microns. The number of chromatids (uncondensed chromosomes) may be 512 to many thousands. Therefore, the salivary gland chromosome is also known as a giant chromosome. The reason behind naming this chromosome is that It contains a high number of chromatids. The salivary gland chromosome (polytene chromosome) contains a Swollen region at some places. These swollen regions are called balbiani rings or puffs. The Polytene chromosome plays a role in regulating the metamorphosis and moulting process of insect larva.