Polytene chromosomes are quite common in salivary glands of insects and so are called salivary chromosomes. These chromosomes have high amount of DNA of almost 1000 times in Drosophila as compared to ordinary somatic chromosomes. These chromosomes are multistranded. They are in permanent prophase stage. These chromosomese are formed by somatic pairing between homologous chromosomes and repeated replication of their chromonemata without separation of chromatids. All the chromosomes may remain attached to one another at a common point called chromocentre.