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

New genes are not formed out of the blue and are always the result of duplication and modification of old genes (XI.2).A haploid genome contains only one copy of each gene and thus the formation of a new gene must be preceded by duplication of an old gene.Both copies are identical after the duplication and thus such a mutation does not bring any benefit for its carrier.Only as a consequence of further mutations can one of the copies acquire a new function and the mutant can then potentially have a selection advantage over its predecessor.Thus, the evolution of a new gene in a haploid organism is dependent on the formation of at least two mutually independent rare events – duplication and mutation.In contrast, in a diploid organism, the “raw material” for the formation of a new gene exists right from the very beginning – the second copy of each gene.If mutation occurs in one copy, causing the product of the gene to begin to fulfill a new function, the mutant can be selected right away.The mutated copy can even cease to fulfill its original function.This is not manifested in any way in heterozygotes; however, homozygotes with two mutated alleles can be unviable.As long as the frequency of mutants in the population is not too high, a large percentage of these homozygotes are not generated during sexual reproduction.However, if the frequency of mutant alleles increases above a certain level, these homozygotes begin to be generated with ever increasing frequency and a selection pressure emerges for duplication of the given locus.Sooner or later, crossing-over occurs between the old and new locus so that the haploid gene of the recombinant progeny will contain the original allele in one locus and the new, mutated allele in a different locus.Thus, the diploid state is renewed, however now with two different independent loci.It is apparent that all the intermediate stages in the formation of a new gene are selectionally preferred over the initial stages in a diploid organism.Evolution of a new gene must take place here at a substantially greater rate than in haploid organisms (Lewis & Wolpert 1979)(see Fig. XI.2).s