Additive Genetic Breeding Values Correlate with the Load of Partially Deleterious Mutations

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Science  14 May 2010:
Vol. 328, Issue 5980, pp. 892-894
DOI: 10.1126/science.1188013

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Pedigree Weevils

The phenotype of an organism is related to its additive genetic phenotype, the small but numerous genetic differences between individuals affecting their phenotype, and its mutational load, which is the number of mutations an individual carries. How these two factors affect an individual's ability to leave offspring in the next generation is a major component of evolutionary theory, but evidence for a direct relationship has been lacking. By estimating the contribution of partially recessive mutations to additive genetic variation in seed-feeding cow-pea weevils over a seven-generation pedigree breeding program involving variation in levels of inbreeding, Tomkins et al. (p. 892) demonstrate an association between genetic quality and the mutational load carried, especially for males.


The mutation-selection–balance model predicts most additive genetic variation to arise from numerous mildly deleterious mutations of small effect. Correspondingly, “good genes” models of sexual selection and recent models for the evolution of sex are built on the assumption that mutational loads and breeding values for fitness-related traits are correlated. In support of this concept, inbreeding depression was negatively genetically correlated with breeding values for traits under natural and sexual selection in the weevil Callosobruchus maculatus. The correlations were stronger in males and strongest for condition. These results confirm the role of existing, partially recessive mutations in maintaining additive genetic variation in outbred populations, reveal the nature of good genes under sexual selection, and show how sexual selection can offset the cost of sex.

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