Salivary gland giant chromosome

In the same way that amphibian oocytes are an accessible scource of giant lampbrush chromosomes (as well as nuclear envelopes), the salivary glands of dipteran larvae are a source of giant polytene chromosomes, which are formed by repeated endomitotic reduplication of the DNA, while retaining lateral association of chromatids. In Chironomus tentans, polytene chromosomes in salivary... 

There is only little evidence of correlation between individual bands and cystrons (Welshons, 1965). The middle-sized chromomere in the giant chromosomes of Chironomus salivary glands contains sufficient DNA for the coding of 100 intermediate-size protein molecules (Edstrom, 1965). 

Giant chromosomes are found, inter alia, in the salivary glands of Dip-/emsuch as Drosophila, Chironomus, Acricotopus, and Sciara. They are bundles of a few thousand homologous chromatids laid down in parallel and, at the same time, slightly skewed like the strands of a rope (Fig. 143). Each chromatid appears to be divided lengthwise chromomeres appear to be strung on the chromonema like a set of beads. 

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