Modifier genes and protective alleles in humans and mice.

Interest in modifier genes is growing rapidly because of their ability to modulate the phenotype of individuals with monogenic and multigenic traits and diseases. A neglected class of modifiers is protective alleles that can suppress disease in otherwise susceptible individuals. Together these modifier genes and protective alleles provide important glimpses into the molecular and cellular basis for the functional networks that provide robustness and homeostasis in complex biological systems.