June 02, 2009

Patterns of natural selection and phenotype convergence in FUT2

This paper shows an example of convergent evolution in humans, in which similarity in an observable trait is explained by different underlying gene variants. Another example of this phenomenon is convergent evolution of skin color with depigmentation of Caucasoids and Mongoloids relative to the African ancestral form occurred due to different mutations, or lactase persistence where the ability to digest milk evolved independently in Europe and Africa.

Molecular Biology and Evolution doi:10.1093/molbev/msp108

A natural history of FUT2 polymorphism in humans

Anna Ferrer-Admetlla et al.


Because pathogens are powerful selective agents, host cell surface molecules used by pathogens as identification signals can reveal the signature of selection. Most of them are oligosaccharides, synthesized by glycosyltransferases. One known example is balancing selection shaping ABO evolution as a consequence of both, A and B antigens being recognized as receptors by some pathogens, and anti-A and/or anti-B natural antibodies produced by hosts conferring protection against the numerous infectious agents expressing A and B motifs. These antigens can also be found in tissues other than blood if there is activity of another enzyme, FUT2, a fucosyltransferase responsible for ABO biosynthesis in body fluids. Homozygotes for null variants at this locus present the non-secretor phenotype (se), since they can not express ABO antigens in secretions. Multiple independent mutations have been shown to be responsible for the non-secretor phenotype, which is coexisting with the secretor phenotype in most populations. In this study, we have resequenced the coding region of FUT2 in 732 individuals from 39 worldwide human populations. We report a complex pattern of natural selection acting on the gene. While frequencies of secretor and non-secretor phenotypes are similar in different populations, the point mutations at the base of the phenotypes are different, with some variants showing a long history of balancing selection among Eurasian and African populations, and one recent variant showing a fast spread in East Asia, likely due to positive selection. Thus a convergent phenotype composition has been achieved through different mutations with different evolutionary histories.


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