Animal genomes contain millions of functionally significant sites in their DNA sequences and are therefore large targets for mutation. Some mutational differences among genomes have individually large effects, but many others have effects too small to allow measurable differences in particular traits to be attributed to them. In theory, the "mutations of small effect" could collectively account for most of the heritable variation in many traits, but whether they actually do is still unknown owing to the difficulty of studying mutations whose effects cannot be seen directly. Using six closely related species of marine invertebrates (Amphipoda: Cyamus) that have lived in unusually well defined and constant environments for more than five million years, this project will develop a sensitive method for characterizing mutations with very small effects. Over thousands of generations, tiny differences in the performances of the small, simple, non-recombining mitochondrial genomes of these animals are predicted to have large, easily detected effects on the sizes and shapes of their genealogies. The abundances of mutations with various different effect sizes will be inferred from the genealogical distortions together with the histories of mutation in each species.
The combined effects of many mutations with individually small effects may influence many traits of scientific, agricultural and medical importance, including disease susceptibilities and patterns of aging, substantially. This work will complement ongoing attempts to understand the genetics of such traits, by revealing the nature and scale of the contributions from small-effect mutations in a simple and well-defined natural system. This award will also support graduate and undergraduate students at the University of Utah and contribute to a GK-12 project already underway in area high schools.
