Possibilities of utilization of isozymes as markers of the activity of genes in ontogenesis are considered. There are cases of both the synchronous and asynchronous activation of paternal and maternal genes controlling the synthesis of appropriate isozymes. The asynchronous activation is peculiar, mainly, of interspecific hybrids. The organospecific pattern of isozymes in ontogenesis is determined not only by the activity of structural genes controlling their syntheses, but also by numerous genes-modificators active at the translation and posttranslation levels.