XI.2 New genes come from extra copies of genes or from expendable old genes

In the further text, a new gene will be considered to be a gene encoding a product, most frequently a protein, with a new biological function.A typical example is the gene for an enzyme that has acquired affinity for a new substrate through mutation.At this point, the mutated allele of a gene that differs from the alleles of a different sequence, but has the same biological properties and is exposed to the same selection pressures as the original allele, will not be considered to be a new gene.

            The formation of a new gene requires primarily selection pressure for the formation of the new gene or, to be more precise, selection pressure that is capable of fixing a randomly formed variant of an old gene, where it provides an advantage for its carrier at the expense of the carriers of the old variant.The second precondition lies in the existence of a material substrate for the formation of a new gene.This substrate is usually an old gene.Through accumulation of mutations, such a gene can be converted into a new gene, where the formation of a new gene and thus the disappearance of the old gene must not lead to loss of or a substantial reduction in the fitness of the carrier of the new gene.s

            Extra copies of an old gene can be the best substrate for the formation of a new gene.However, a gene located in a single copy in the haploid genome can also act as a substrate, assuming that this is not a gene that is of vital importance for the given organism at the particular moment.Accumulation of mutations as a consequence of selection pressure for optimization of the new biological function of a new gene most probably leads to a gradual deterioration in the biological function originally fulfilled by the product of the particular gene.This follows both from the logic of the mater (it also holds for enzymes that it is difficult to serve two masters) and this is also demonstrated by the properties of contemporary enzymes.During evolution, tens of thousands of specialized enzymes are generally formed, rather than accumulation of biological functions on individual multifunctional enzymes.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.