[Conditional lethal mutations shift the genome from stability to instability].

The phenomenology of genomic destabilization is described in Drosophila melanogaster mutants containing radiation-induced conditional dominant lethals in the X chromosome and in autosome 2. Destabilization manifests itself as (1) the loss or decrease of lethality of previously lethal mutations; (2) the loss of expression of visible dominant mutations in an opposite homolog; (3) chromosomal instability resulting in the loss of the X chromosome in germline and somatic cells; (4) the occurrence of novel mutations (secondary mutagenesis); (5) the occurrence of single and mass modifications; (6) disturbances in individual development (formation of morphoses). The key event for the shift of the genome from the stable state into the unstable one is the occurrence of a conditional dominant lethal mutation.