RNA tumor virus genes and the transforming genes: genetic transmission, infectious spread, and modes of expression.

The genetic conservation and evolution of virogenes in mammalian species are described in relation to the horizontal, vertical, and congenital transmission of type C RNA oncogenic viruses within members of a given species, or among members of near and/or distantly related species. Examples of oncogenic virus infection between ancestors of the mouse, cat, pig, and primates as well as the integration of the virus into the host's genome are documented. The possible normal functions of the virogenes as a part of the cellular genome of many species are explored. Recent evidence of genetic recombination (genetic mixing) among distinct type C viruses is also reviewed, thus completing an overview of the evolutionary past, present, and complex future relationships of oncogenic RNA viruses and mammalian species.