They are the only group of single stranded RNA viruses that can incorporate themselves into the host cell genome. They can not complete their replication cycle in the cytoplasm of the host cell like some other single stranded RNA viruses. X Retroviruses combine the characteristics of DNA and RNA viruses. They control the expression of structural genes by allowing or preventing the translation of mRNA at the ribosome. X Repressor substance, produced by the regulator gene, must bind to the operator to prevent expression of the structural genes.
Transcription occurs when the repressor substance is bound to the promoter gene.
X A mutagen in the environment produces an advantageous nonlethal mutation. X A bacteriophage brings an R plasmid into a daughter by transduction. The daughters replicate their chromosome using the theta replicon. Soak it in a sanitizer and rinse it with a bleach solution. X Wash it with hot, soapy water and soak it in gluteraldehyde overnight.