Abstract
A polygenic system of expression of the quantitative character radius incompletus was shown to be sensitive to external and physiological stresses: heat shock, gamma-irradiation, isogenization, etc. This stress response involved mobilization of retrotransposons. Heavy heat shock induced transpositions of Dm412 and B104 in three and one isogenic lines, respectively. The induced transposition rate was (2.5-11.0) x 10(-2) per site per sperm per generation, i.e., 1-2 orders of magnitude higher than for spontaneous transpositions. Induction of transpositions by gamma-radiation yielded similar estimates. Recently, induction of transpositions and excisions by isogenization was demonstrated; transposition and excision rates were, respectively, 0.35 and 0.13 per site per sperm per generation, which was 2-3 orders of magnitude higher than in control lines. In all these cases, stress induction of retrotransposon transpositions was mediated by molecular mechanisms of the heat shock system-the general system of cell resistance to external and physiological stress factors. From the viewpoint of evolution, stress induction of transpositions is a powerful factor generating new genetic variation in populations under stressful environmental conditions. Passing through a "bottleneck," a population can rapidly and significantly alter its population norm and become the founder of new, normal forms.
