Patterns of puffing activity and chromosomal polymorphism in Drosophila subobscura. IV. Position effect at the boundaries of the E12 inversion.

The puffing patterns in polytene E chromosomes of Drosophila subobscura were followed in third-instar larvae and throughout the prepupa period. Two gene arrangements, Est and E1+2+9+12 were studied. A majority of puffs exhibit a similar pattern, but the puffs 61AC and 67AB behave differently in the two chromosomal arrangements, both in homozygotes and in heterozygotes. These two puffs are located at the end of the E12 inversion. This position effect is an interesting phenomenon that probably is not due to a heterochromatinization effect.