Base Composition Patterns


Genomic GC content varies both between species and within individual genomes. The nature of this variation differs between groups of organisms. Bacteria exhibit little intragenomic variation in GC content, but a large range of variation between species. In contrast, higher eukaryotes exhibit a much narrower range of variation in GC content between species, but many have highly structured variation within their genomes, which may reflect a fundamental level of genome organisation. The causes of variation in GC content have been subject to debate, and it has been suggested that both natural selection and mutational biases may play a role. However, at least in vertebrates, much recent evidence points to a strong role of recombination in determining base composition patterns.

Key Concepts:

  • GC content shows considerable variation between species and within genomes.

  • GC content is rarely at equilibrium, and changes over evolutionary time.

  • Recent evidence points to a strong role of recombination in determining GC content.

Keywords: base composition; GC content; molecular evolution; population genetics; mutation; selection; biased gene conversion

Figure 1.

The distribution of genomic G+C content in seven groups of organisms. Bacteria, fungi, algae and protozoa panels redrawn from Bak AL, Atkins JF, Meyer SA, Singer CE and Ames BN (1972) Evolution of DNA base compositions in microorganisms. Science 175: 1391–1393. Other data from Shapiro HS (1976) In Fasman GD (ed.) CRC Handbook of Biochemistry and Molecular Biology. Cleveland: CRC Press.

Figure 2.

Examples of compositional variation in six divergent eukaryotes (Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, Gallus gallus and Homo sapiens). Data is plotted as average GC‐content in sliding windows of 100 kb, moving at 10 kb intervals.



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Further Reading

Berglund J, Pollard KS and Webster MT (2009) Hotspots of biased nucleotide substitutions in human genes. PLoS Biology 7: e26.

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Axelsson, Erik, and Webster, Matthew T(Apr 2011) Base Composition Patterns. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001805.pub2]