The biological importance of measuring individual variation.

Functional genomics research using Fundulus heteroclitus has focused on variation among individuals because of the evolutionary importance and value of Fundulus in explaining the human condition (why individual humans are different and are affected differently by stress, disease and drugs). Among different populations and species of Fundulus, there are evolutionarily adaptive differences in gene expression. This natural variation in gene expression seems to affect cardiac metabolism because up to 81% of the variation in glucose utilization observed in isolated heart ventricles is related to specific patterns of gene expression. The surprising result from this research is that among different groups of individuals, the expression of mRNA from different metabolic pathways explains substrate-specific metabolism. For example, variation in oxidative phosphorylation mRNAs explains glucose metabolism for one group of individuals but expression of glucose metabolism genes explains this metabolism in a different group of individuals. This variation among individuals has important implications for studies using inbred strains: conclusions based on one individual or one strain will not necessarily reflect a generalized conclusion for a population or species. Finally, there are surprisingly strong positive and negative correlations among metabolic genes, both within and between pathways. These data suggest that measures of mRNA expression are meaningful, yet there is a complexity in how gene expression is related to physiological processes.