IX.4.3.1 Step changes in substitution rate can be related to a change in the gene function or to a change in the number of its copies in the genome

A substantial change in the substitution rate can occur, for example, when the product of a certain gene begins to fulfill a new function in a particular organism or when this gene is duplicated and the organism obtains a second copy in its genome.In this case, the intensity of selection, to which the given gene is exposed, changes drastically; this can increase or reduce the substitution rate in the given DNA section.Extensive studies performed on baker’s yeast have shown that genes, whose deletion has no great effect on the viability of the organism, exhibit a greater substitution rate (Hirsh & Fraser 2001).

            Consequently, it holds in general that it is advantageous to select for analysis a section of such a gene that fulfills the same function in all taxa and is thus exposed to the same selection pressures during evolution.Consequently, for example, genes coding a protein of the replication, transcription or translation apparatus are frequently used.However, because selection at a single site on the chromosome affects the probability of fixation of selectively significant and selectively neutral mutations occurring in adjacent regions as a consequence of genetic draft, a change in the function of one gene can substantially affect the substitution rate in adjacent DNA sections.Thus, the only effective strategy for dating cladogenetic events remains to use the results of analysis of a greater number of genes that are independent both from the perspective of function and from the perspective of genetic linkage.

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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.