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chromosome puff[′krō·mə‚sōm ‚pəf]
in cytogenetics, a swelling that is found on polytene chromosomes; an aggregate of puffs corresponds to a set of active, or functioning, cellular genes at a given stage of the cell’s differentiation.
The development of chromosome puffs is related to the despiralization of chromonemata, or the threads that are the structural units of chromosomes. In most cases, puffs are formed within a single disk, although there are complex puffs that include 4 to 20 disks. Large puffs with complex structures are called Balbiani rings.
The formation of chromosome puffs has been studied in detail in representatives of dipteran insects, for example, in Tendipedidae and Drosophila. At various stages of larval development in these insects, there is a regular shift in the location of puffs on the same chromosomes. This is evidence that separate areas of a chromosome function relatively independently.
It has been shown that the biosynthesis of deoxyribonucleic acid (DNA) occurs in puffs, as does the intensified synthesis of proteins and messenger ribonucleic acid (mRNA). The study of the dynamics of puff formation makes it possible to understand how a chromosome set, which is theoretically similar in all body cells, participates in the differentiation of various cell systems. Chromosome puff formation is mainly controlled genetically, although other factors are also involved, including those that are physiological. The development of new puffs as a result of mutations or under the influence of such factors as hormones and temperature has created broad possibilities for experimenters to direct the development and differentiation of multicellular organisms.
A phenomenon similar to puffs is observed in lampbrush chromosomes, which were discovered during the formation of egg cells in birds, fishes, reptiles, and amphibians. Certain areas of this type of chromosome are strongly despiralized and form loops with an increased functional activity (synthesis of RNA and protein).
M. M. ASLANIAN