Most gerontological research is conducted using inbred strains of animals in an attempt to maximize phenotypic uniformity within experiments and thus increase the experimenter's statistical power to detect treatment effects. However, for a wide range of phenotypic traits, F1 hybrids between inbred strains are considerably less variable than the parental inbred strains themselves. Therefore, the use of F1 hybrids is preferable for many research applications. In this article, we discuss the sources of phenotypic variability and explain why F1 hybrids are often less variable than inbred strains; we review the empirical literature illustrating the large range of species and traits for which this is true; and finally we suggest how this finding suggests that F1 hybrids may often be superior animal models for studying the aging process and how to manipulate it.
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