Selection limits

and possibly unique mutations, but, overall, did not change in their average phenotype from the beginning of the experiment. Both of the high-selected lines reached apparent selection limits around generation 20. Both of the low-selected reached absolute limits near zero around generation 25. A selection limit is a term from animal breeding and quantitative genetics that refers to a cessation of progress even when continued directional selection is being applied to a trait, such as body size. In other words, a breeder or scientist is using selective breeding (artificial selection) and choosing individuals as breeders within a population based on some phenotypic trait or traits. If this is done, then the average value of the population typically evolves across generations in the direction being favored by selection (i.e., for higher or lower values of the trait), but then at some point the population stops evolving. The trait under selection is then said to have reached a limit or plateau at that value.

and possibly unique mutations, but, overall, did not change in their average phenotype from the beginning of the experiment. Both of the high-selected lines reached apparent selection limits around generation 20. Both of the low-selected reached absolute limits near zero around generation 25. A selection limit is a term from animal breeding and quantitative genetics that refers to a cessation of progress even when continued directional selection is being applied to a trait, such as body size. In other words, a breeder or scientist is using selective breeding (artificial selection) and choosing individuals as breeders within a population based on some phenotypic trait or traits. If this is done, then the average value of the population typically evolves across generations in the direction being favored by selection (i.e., for higher or lower values of the trait), but then at some point the population stops evolving. The trait under selection is then said to have reached a limit or plateau at that value. ==Experiments to identify causes of selection limits== Experimental approaches to probe the causes of selection are of two general types, quantitative genetic and functional. The former asks general questions about the genetic architecture of the trait when a limit has been attained (e.g., has narrow-sense heritability gone to zero?), whereas the latter attempts to determine what aspect of physiological or other function might have reached a limit or constraint. Experimental studies may involve attempts to break an apparent selection limit. As an example of a genetic approach, two replicate lines of mice at a limit for large nest size were crossed and selection was continued on this new population, resulting in further increase in nest size. From a functional perspective, in lines of mice at a selection limit for high wheel running, administration of an erythropoietin analog increased the maximal rate of oxygen consumption during forced exercise, but did not increase wheel running, a result suggesting that motivation for exercise may be limiting the behavior, rather than inherent ability to run on wheels. ==See also== Bill Hill (geneticist) I. Michael Lerner Kenneth Mather Douglas Scott Falconer Experimental evolution Plant breeding ==References==

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