Temporal Control of Puffing Activity in Polytene Chromosomes

The genetic organization of individual bands of polytene chromosomes is an enigma. On the one hand, we have evidence (Rudkin, 1965; Daneholt and Edström, 1967; Mulder et al, 1968; see also Rasch et al., 1971) that an “average” band contains DNA equivalent to 40,000 or so nucleotide pairs. The range is perhaps between 3000 and 100,000 nucleotide pairs (Beermann, 1972). On the other hand, classical (e.g., Painter, 1934; Bridges, 1935, 1936; Mackensen, 1935; Muller and Prokofyeva, 1935) and more modern (e.g., Hochman, 1971; Lefevre, 1971; Lim et al., 1971; Judd et al., 1972; Rayle, 1972) evidence strongly suggests that one band (or band plus adjacent interband(s), if you will: Crick, 1971) corresponds to a unit of genetic function.