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

In this test, two mutants with mutations manifested in the same way in the phenotype of their carriers are first prepared or isolated from nature. If we are interested in whether both mutations are found in the same cistron, then a sufficiently long continuous DNA section bearing the mutation is transferred artificially, e.g. through transfection, or naturally, i.e. through crossing, from one mutant to cells containing the DNA of the individual with the other mutation. The obtained individual carries the given section in two copies, each of which bears one mutation. If the functioning of the particular gene is renewed in it, i.e. the original form of the trait corresponding to the unmutated form of the given gene is formed, it will be very probable that the relevant mutation will be located on two different cistrons. In the opposite case, this will correspond to a mutation on a single cistron. This test can be employed in this simple manner only if the wild form of the trait is dominant, i.e. when the presence of only a single copy of the given gene in the genome is required for its occurrence. Simultaneously, it is necessary to exclude (technically in advance or at least subsequently when evaluating the data) the possibility that the functioning of the given gene was renewed as a consequence of genetic recombination occurring directly in the studied DNA section. See also Gene