Any of a group of RNA .
Retroviruses are responsible for some cancers and viral infections of animals, and they cause at least one type of human cancer. The retrovirus HIV is the cause of AIDS in humans. The name signifies that they use RNA to synthesize DNA , the reverse of the usual cell process. This process makes it possible for genetic material from a retrovirus to enter and become a permanent part of the {{link=gene">genes of an infected cell.