Uncovering cryptic genetic variation

Key PointsCryptic genetic variation (CGV) is genetic variation that is not normally expressed, but that is available to modify abnormal phenotypes produced by environmental or genetic perturbation.CGV is relevant to understanding the expressivity of disease phenotypes, mechanisms of animal and plant breeding, and the relationship between macro- and micro-evolution.CGV is thought to arise as a result of unusually large genotype-by-environment and/or genotype-by-genotype (epistatic) interactions.Threshold-dependent effects might help to hide CGV in natural populations.Some alleles that contribute to CGV might modify standing variation for different (pleiotropic) traits, but in general, the factors that help to maintain CGV are unknown.The same tools that are used to examine visible complex phenotypes can be used to examine CGV, including complementation testing, quantitative trait locus mapping and association studies.