Coronaviruses are RNA-containing viruses. The genome of coronaviruses is represented by the RNA molecule that is replicated in host cells via viral RNA-dependent RNA polymerase. RNA is less stable than DNA, whereas RNA-dependent RNA polymerase is less accurate than DNA-dependent RNA or DNA polymerases. As a result, the enzyme activity results in the production of numerous mutated RNA molecules. Although most of the viral particles that contain mutated RNA are nonviable, a large portion of mutated viruses can infect host cells resulting in the production of new viruses. Moreover, the mutated RNA encodes proteins with new properties, i.e., receptor specificities. As a result, these new viruses can attach to similar but distant receptors that can be found in different species. A phenomenon is observed in the flu virus and human immunodeficiency virus that are RNA-containing viruses and are also characterized by a high level of mutations.