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(1) Change in the means of reproduction in organisms during two or more generations; a particular case of alternation of generations.
(2) The sudden appearance of individuals differing sharply in a number of traits from the parent forms. This phenomenon served as the basis for the appearance of the heterogenetic theory of the origin of species by means of the sudden appearance of individuals differing sharply from the parent forms. (This theory was proposed by the German histologist R. A. von Kölliker in 1864 and the Russian botanist S. G. Korzhinskii in 1899.)