POPULATION-DYNAMICS OF THE RESPONSE OF THE DM412 GENOMIC PATTERN TO SELECTION FOR A QUANTITATIVE TRAIT IN DROSOPHILA

In an isogenic line of Drosophila melanogaster carrying the Mendelian mutation radius incompletus, selection for the total length of two seg ments of the disrupted longitudinal wing vein was conducted. After gam ma-irradiation at a dose of 13 Cy, positive and negative truncation se lection became highly effective and was completed in 50 generations. T he pattern of mobile genetic element Dm412 was almost completely fixed in the course of selection. In the positive direction of selection, f ixations of mobile genetic element (MGE) sites exceeded losses; in the negative direction, this relationship was reversed. The number of MGE sites in the pattern increased from 23 to 33 and to 26 in the positiv e and negative directions, respectively. The mean heterozygosity of MG E sires decreased respectively ten and six times, The dynamics of some sites (6F, 43B, 66A, 69E, and others) corresponded to that expected w ith an adaptive response to selection. Two out of these sites (43B and 66A) were previously assigned to hot sites of Dm412 transposition ind uced by heat shock. Fixation and loss of sites continued on average fo r tens of generations, Four hypotheses describe the relationship betwe en patterns of polygenes and MGE in the context of explanation of the above facts: (1) genetic drift; (2) the linkage of MGE and polygenes w ithout modification of the latter (hitchhiking); (3) the linkage and m odifying effect of MGE on polygenes linked with them; (4) the selectio n of the ''champion'' pattern of polygenes and a random or adaptive MG E pattern linked with it. Hypotheses 1 and 2 are unlikely, hypothesis 3 is possible in the case of other selection modes, whereas hypothesis 4 seems to be most plausible.