Comparative study of the function of polytene chromosomes in laboratory stocks of Drosophila melanogaster and the l(3)tl mutant (lethal tumorous larvae)

A study of the puffing pattern of the salivary gland autosomes of D. melanogaster was performed through the last 24 hours of larval development and 0-hour prepupae. Since both prominent and small puffs were taken into account, the total puff number amounted to 275. Of these, 116 are almost constant in size during the 24 hours observation period, 106 increase in size or appear before pupation. 37 puffs are active in 96 hour larvae and disappear or decrease sharply in size by 115–118 hours. 12 biphasic puffs have been found with higher activity in 96 hour larvae and 0-hour prepupae and lower activity by 115–118 hours. Three extremely irregular puffs have been detected in chromosome 4. The data obtained evidence that a larger number of D. melanogaster polytene chromosome loci are active during larval development than it has been thought earlier. It has also been shown that only 38% of autosomal puffs change before the beginning of metamorphosis. The functional significance of small puffs and strain specificity of puffs are discussed.