Puff region of giant chromosome. Coloured Scanning Electron Micrograph (SEM) of the puff region of a giant chromosome. This giant chromosome occurs in the salivary gland of the midge insect Chironomus sp. (family: Chironomidae). The puff region is an expanded area of DNA (Deoxyribonucleic acid). The giant size of this chromosome, easily seen at low magnification, is a condition known as polyteny. Polyteny occurs when parallel copies of the chromosome are formed but these copies fail to separate and instead form puffs and banding patterns. This form is an advantage to geneticists who can study the function of these chromosomes. Magnification: x4,800 at 5x7cm size. x16,500 at 8x10 inch size