The rate of spontaneous mutation is a key parameter in modeling the genetic
structure and evolution of populations. The impact of the accumulated load
of mutations and the consequences of increasing the mutation rate are impo
rtant in assessing the genetic health of populations. Mutation frequencies
are among the more directly measurable population parameters, although the
information needed to convert them into mutation rates is often racking. A
previous analysis of mutation rates in RNA viruses (specifically in ribovir
uses rather than retroviruses) was constrained by the quality and quantity
of available measurements and by the lack of a specific theoretical framewo
rk for converting mutation frequencies into mutation rates in this group of
organisms. Here, we describe a simple relation between ribovirus mutation
frequencies and mutation rates, apply it to the best (albeit far from satis
factory) available data, and observe a central value for the mutation rate
per genome per replication of mu(g) approximate to 0.76.(The rate per round
of cell infection is twice this value or about 1.5.)This value is so large
, and ribovirus genomes are so informationally dense, that even a modest in
crease extinguishes the population.