[Role of genetic processes in modification variability. Prophecy of B.L. Astaurov]

In his pioneering work on mutation tetraptera in Drosophila melanogaster, B.L. Astaurov discovered spontaneous modifications based on variability in gene expression. This new approach to the phenomenon of modifications should be considered as the first stimulus to development of the general theory of variability. Contemporary classification of variability based predominantly on phenomenology encounters many contradictions. The same specific molecular mechanisms may be responsible, for example, for both hereditary and nonhereditary variability depending on the taxonomic status. Some mechanisms responsible for both mutations and modifications or for mutations, recombination, and ontogenetic variability have been considered from this viewpoint. It may well be more productive to consider different types of variability with respect to the main genetic processes: replication and expression of genetic material.