Giant chromosome. Coloured scanning electron micrograph of a giant chromosome from the salivary gland of the non-biting midge insect Chironomus sp. (family: Chironomidae). The surface structure of the chromosome is seen, with twists, banding pattern and puffs. The enormous 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 from one another. This is an advantage to geneticists intent on studying the structure and function of chromosomes. Magnification: x960 at 6x6cm size.