Evolution by gene duplication

Evolution by gene duplication is understood to be an important source of novelty in evolution, providing for an expanded repertoire of molecular activities. The underlying mutational event of duplication may be a conventional gene duplication mutation within a chromosome, or a larger-scale event involving whole chromosomes (aneuploidy) or whole genomes (polyploidy). A classic view, owing to Susumu Ohno, is that duplication creates redundancy, and redundancy provides fuel for innovation. Knowledge of evolution by gene duplication has advanced more rapidly in the past 15 years due to new genomic data, more powerful computational methods of comparative inference, and new evolutionary models.

Several models exist that try to explain how new cellular functions of genes and their encoded protein products evolve through the mechanism of duplication and divergence. Although each model can explain certain aspects of the evolutionary process, the relative importance of each aspect is still unclear. This page only presents which theoretical models are currently discussed in the literature. Review articles on this topic can be found at the bottom.

In the following, a distinction will be made between explanations for the short-term effects (preservation) of a gene duplication and its long-term outcomes.

Since a gene duplication occurs in only one cell, either in a single-celled organism or in the germ cell of a multi-cellular organism, its carrier (i.e. the organism) usually has to compete against other organisms that do not carry the duplication. If the duplication disrupts the normal functioning of an organism, the organism has a reduced reproductive success (or low fitness) compared to its competitors and will most likely die out rapidly. If the duplication has no effect on fitness, it might be maintained in a certain proportion of a population. In certain cases, the duplication of a certain gene might be immediately beneficial, providing its carrier with a fitness advantage.

The so-called 'dosage' of a gene refers to the amount of mRNA transcripts and subsequently translated protein molecules are produced from a gene per time and per cell. If the amount of gene product is below its optimal level, there are two kinds of mutations that can increase dosage: increases in gene expression by promotor mutations and increases in gene copy number by gene duplication.

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