Biased Gene Conversion and Its Impact on Genome Evolution

Abstract

In most eukaryotes, genetic information is exchanged between homologous chromosomes via the process of recombination. As part of this process, short deoxyribonucleic acid (DNA) tracts of less than 1 kb in length are exchanged between chromosomes in an asymmetric fashion in a process known as gene conversion. When such gene conversion events occur within the vicinity of heterozygous loci, this asymmetric exchange of DNA can result in the non‐Mendelian transmission of alleles. Multiple lines of evidence suggest that this non‐Mendelian transmission is biased in favour of G and C alleles at the expense of A and T alleles. This process, known as biased gene conversion, has a number of important implications for understanding the behaviour of alleles within a population and the base composition of the genome itself.

Key Concepts:

  • Biased gene conversion is the preferential transmission of certain alleles to the next generation, arising from asymmetries in the gene conversion process.

  • Biased gene conversion appears to preferentially favour GC alleles over AT alleles, resulting in the overtransmission of GC alleles in regions of high recombination.

  • Biased gene conversion can increase the frequency of an allele in a population.

  • Consistent biased gene conversion can ultimately influence the base composition of the genome, leading to increased levels of GC content.

  • Although a difficult phenomenon to measure, multiple lines of experimental and evolutionary evidence support the existence of biased gene conversion.

Keywords: recombination; biased gene conversion; GC content; evolution; substitution rate

Figure 1.

The effect of biased gene conversion (BGC) on genetic drift. The figure shows the effect of BGC on the frequency of the driven allele over time. Red lines show frequencies simulated with BGC, whereas the black lines show simulations conducted without BGC. Faint lines show five independent simulations in each case, whereas thick lines show the theoretical expectation. Data was simulated for a population size of 10 000 with a starting allele frequency of 5%, and a very strong bias parameter (δ) of 0.5%, chosen for illustration purposes.

Figure 2.

Cartoon representation of a possible biased gene conversion mechanism. A double‐strand break in the vicinity of a G/A polymorphism results in the partial loss of the A/T base pair on the second chromosome. The subsequent heteroduplex formed following strand invasion contains a mispairing between the G and T nucleotides. biased gene conversion results from the biased repair of this mismatch, which tends to favour the G allele over the T allele. © PLoS.

Figure 3.

Increased GC substitution rates around human hotspots. Recombination hotspots are localised regions of approximately 2 kb width in which the recombination rate can be hundreds or thousands of times that of the surrounding region. This figure shows an increased rate of GC substitutions can be observed on the human lineage in the vicinity of human hotspots. However, as recombination hotspot positions are not shared between humans and chimps, no corresponding increase is seen on the chimpanzee lineage. Modified from Auton et al. ().

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Clement Y and Arndt PF (2013) Meiotic recombination strongly influences GC‐content evolution in short regions in the mouse genome. Molecular Biology and Evolution 30(12): 2612–2618.

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Spencer CC, Deloukas P, Hunt S et al. (2006) The influence of recombination on human genetic diversity. PLoS Genetics 2(9): e148.

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How to Cite close
Bhérer, Claude, and Auton, Adam(Jun 2014) Biased Gene Conversion and Its Impact on Genome Evolution. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020834.pub2]