Assortative mating and hypervariability as the result of genomic stress, caused by selection, appear the main components of the mechanism of intrapopulation polymorphism maintenance. Activation of genome transposable elements has contributed significantly to increasing of variability provoked by inbreeding. Copy number of transposone Hermes DNA evaluation in somatic tissues of Musca domestica individuals from the strains differ by the life span at all developmental stages used as the criterion of genome stability. Investigations funded by RFBR 12-04-01450-a and 11-04-97005-r_povolzhje_a.