Synthetic Activity of Polytene Chromosomes

Abstract

Publisher Summary This chapter describes the synthetic machinery producing the two most important categories of macromolecules in living organisms, DNA and RNA. Polytene chromosomes, especially those of Diptera are excellent and unique tools for studies on genetic problems in conjunction with chromosome cytology in higher organisms. In Diptera, polyteny is widespread among larval tissues (including esophagus; salivary glands; fore-, mid-, and hindgut; gastric ceca, Malpighian tubules; fat body; tracheal wall cells; muscle; and certain types of cell in the nerve ganglia), but it can also be observed in some tissues and special cell types of the pupa (trichogen and thormogen cells present in developing bristle sockets and certain cells in the epidermis of the footpads, or pulvilli of the pretarsus) and in the adult (Malpighian tubules and ovarian nurse cells). The development of techniques for the isolation of distinct chromosome parts, and techniques for in situ nucleic acid hybridization, have illustrated the manifold opportunities offered for studies on the synthetic activities of the genome by utilization of cytological and biochemical methods. Polytene chromosomes promise to play an important role in the clarification of the investigations related to the mechanisms by which genetic information in the eukaryotic cell is handled during growth and development.