Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Muller’s ratchet can cause problems for viruses, which do not reproduce sexually.A large number of individuals in the population and large number of progeny formed by reproduction of one virus can be a certain defense against Muller’s ratchet.Both permit very effective selection, which is capable of eliminating even relatively slightly negative mutations.In viruses with a segmented genome, i.e. with a genome formed by several separate nucleic acid molecules, another mechanism contributes to this effect, complementation and the associated virus reactivation (Bernstein et al. 1985; Turner 2003).Experiments have shown that viruses whose nucleic acid has been exposed to the action of properly selected concentrations of a mutagen are not capable of reproducing in the affected cell under normal conditions.The genome of at least one of them contains a lethal mutation in at least one of its segments.However, if the cell is infected by a large number of viruses, they mutually functionally complement one another (trans-complementation), as any one segment of the genome is functional in at least one virus.Simultaneously, a sort of genetic recombination occurs; segments of the virus genome derived from various viruses are quite randomly wrapped into newly formed virus particles.A certain number of the new virions thus necessarily acquire a combination of undamaged segments and are capable of further, independent existence.This mechanism of reactivation of damaged viruses can function only in organisms with an extremely small genome, as the percentage of functional recombinants would be negligibly small in organisms with a larger genome.