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Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene .
Evolution by gene duplication is an event by which a gene or part of a gene can have two identical copies that can not be distinguished from each other. This phenomenon is understood to be an important source of novelty in evolution, providing for an expanded repertoire of molecular activities.
A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. One such family are the genes for human hemoglobin subunits; the ten genes are in two clusters on different chromosomes, called the α-globin and β-globin loci.
This gene duplication has created a copy number variation. The chromosome now has two copies of this section of DNA, rather than one. Copy number variation (CNV) is a phenomenon in which sections of the genome are repeated and the number of repeats in the genome varies between individuals. [1]
Subfunctionalization is a neutral mutation process in which each paralog retains a subset of its original ancestral function. The figure illustrates that the ancestral gene (orange & blue) is capable of both functions before gene duplication. After gene duplication the functional capabilities are divided amongst the gene copies.
Top: An ancestral gene duplicates to produce two paralogs (Genes A and B). A speciation event produces orthologs in the two daughter species. Bottom: in a separate species, an unrelated gene has a similar function (Gene C) but has a separate evolutionary origin and so is an analog.
However, the amount of DNA or the number of genes can also increase within an organism through gene duplication, a major mechanism through which new genetic material is generated during molecular evolution. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.
The main source of genetic redundancy is the process of gene duplication which generates multiplicity in gene copy number. A second and less frequent source of genetic redundancy are convergent evolutionary processes leading to genes that are close in function but unrelated in sequence (Galperin, Walker & Koonin 1998).