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

If a group of genes is located next to one another on the chromosome then, in a short time scale, they act as a single gene during genetic processes. This is advantageous in cases when the relevant gene participates in the formation of traits that exist in two or more forms that are advantageous for their carrier, where other forms of the trait that could be formed by random combination of the alleles in the relevant loci would be disadvantageous for their carrier. The occurrence of genes in closely neighbouring loci is then denoted as a supergene.

The best known cases of supergenes were described in study of mimesis in butterflies (see also XVIII.7). Sometimes, a certain type of butterfly imitates several various kinds of poisonous or bad-tasting butterflies. A number of genes affecting the individual traits of the pattern are required for the creation of the relevant pattern on its wings. These genes are located close to one another on the chromosome, so that the parent passes on the relevant combination of alleles to its progeny together. Thus, the progeny consist almost entirely of individuals that inherit the relevant supergene from the father (and imitate one bad-tasting species of butterfly) or who inherited this supergene from the mother (and imitate another species of bad-tasting of butterfly). Individuals that inherited the recombined genotype, whose phenotype would thus not be similar to either of the imitated species and whose mimetic defense against predators would thus be reduced, occur in the progeny of the particular species only rarely.

Like any other property of living organisms, the arrangement of genes on the chromosome is the object of biological evolution. If it is advantageous from the standpoint of the average fitness of progeny that a combination of alleles in a certain group of loci be inherited at once then, in time, mutants are selected in which the relevant genes came very close together as a result of chromosome rearrangements (Sheppard 1958). In some cases, inversion finally occurs in the area in which the relevant supergene is located, leading both directly to reducing the frequency of recombination in the given area between the carriers of various alleles of the relevant supergene and also enabling selection against any recombinants at the level of the precursors of the sex cells, i.e. elimination of cells in which defects in nuclear division could occur as a consequence of recombination in the area with the inversion. Selection at the level of sex cells or their precursors is, of course, much more advantageous than selection at the level of adult individuals from the standpoint of the biological fitness of the individual and thebiodemographic parameters of the population (life history, characters). The creation of molecular mechanisms for its effective functioning, for example the creation of an apparatus for generating local inversions, can become the subject of evolution.