The conditional mutations in D. melanogaster are produced by gamma-irradiation, maintained in laboratory cultures, and inherited as gene mutations. However, their manifestation differs from the conventional mutations by several specific features. The most noticeable specific feature is their conditional nature, i.e., a conditional mutation manifests itself in the individuals of a certain genotype being silent in the individuals with another genotype. A particular procedure for mutation recovery determines what these genotypes will be. An overwhelming number of mutations are conditional dominant lethals. The viable mutation carriers display a drastically decreased fertility. Early zygotic lethality is inherited according to parental type (maternal or paternal). The carriers of conditional mutations give the offspring with a high rate of monstrosities. The possibility for the offspring to form monstrosities is inherited according to a parental (maternal or paternal) type. The level of fertility of conditional mutants is altered by chromosomal rearrangements. The chromosomal rearrangements themselves cause a decrease in fertility. Lethality of the progenies produced by the parents carrying rearrangements is inherited according to a parental (maternal or paternal) type. The results allow for a set of logical arguments in favor of that 1) the genome has a specialized system of genes (ontogenes) that control the course of individual development; 2) unlike a classical gene, acting according to the scheme DNA à RNA à protein, the ontogene implements the regulation according to the scheme DNA à RNA; and 3) the course of individual development is programmed by double-strand RNAs produced by ontogenes in germline cells.