Figure 4. A scenario of fitness between traits at a pleiotropic locus.

When considering differential dominance effects (as seen at DMetS6c) and the relationship not only among the genotypes, but also between insulin and glucose (as illustrated in Figure 2b), it is tempting to speculate that directional selection for the synthetic trait of “fitness” could result in balancing selection at a locus that would favor alleles contributing to low levels of both insulin and glucose. This is illustrated in the ‘Ideal’ quadrant representing relatively low levels of both insulin and glucose.