Isoenzyme frequencies in long-term selection lines of Drosophila melanogaster II. Isoenzyme frequencies of Leucine Aminopeptidases (LAP) in selection lines under different temperature conditions.

1) Permanent population lines of Drosophila melanogaster, derived from a double cross of 4 laboratory stocks, were selected under different temperature conditions (18 °C and 28 °C) for at least 125 generations. 2) The isoenzymes of the leucine aminopeptidases (LAP) controlled by two closely linked loci on the third chromosome were investigated: LAP-A-locus in position 98.0 and LAP-D-locus in position 98.3. Thus the frequency of linkage groups could be estimated by the isoenzyme patterns. 3) In the laboratory stocks the linkage groups A(O)D(F) , A(F)D(F) , A(S)D(S) , A(O)D(S) and A(S)D(F) were present. For the selection lines and reference line the last two linkage groups were absent. 4) The reference line had maintained an allele polymorphism with the frequencies of the linkage groups: p=0.145 for A(O)D(F), q=0.605 for A(F)D(F), and r=0.250 for A(S)D(S) . The reference line had lost the linkage groups A(O)D(S) and A(S)D(F). This fact can be explained by a change of the gene pool in the first generations after the double cross. 5) The selection lines differed from the reference line by higher frequencies of the linkage group A(S)D(S). 6) Among the selection lines the frequencies were not very different. Selection showed only small effects. All selection lines had reacted to selection in the same way: the linkage group A(F)D(F) increased and the linkage group A(S)D(S) decreased. 7) A high frequency of the silent allele A(O) was observed in all lines. The maintenance of this allele can not be explained as yet.