salivary gland chromosome


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salivary gland chromosome

or

polytene chromosome

a giant chromosome present in the salivary glands of certain DIPTERANS, such as midges or fruit flies. The interesting feature of such structures is that, when suitably stained, their CHROMOMERES are readily visible, making it possible to map the physical presence of genes. Studies have shown a clear correlation between the order of genes mapped by genetic RECOMBINATION and visible structures on the polytene chromosomes. At certain times it is possible to see CHROMOSOME PUFFS which are thought to represent areas of gene action.