Repressed Mutation

A "deactivated" mutation. You hold the genes for a mutation, but the mutation does not expresses or manifests itself in your body, it's "dormant", or "silent". Hence, you cannot use a mutation's powers while it is in a repressed state.
In this sense, you may have the genes for a specific mutation, and you may not know it. You may realize it only after you suffer Stress Induction.
You may pass a repressed mutation on to your offspring, even mutations that you don't know you have.

The term can be used as a verb, as "repressing", referring to the act of "deactivating" a previously "activated" mutation (an Expressed Mutation).
It is unlikely an expressed mutation becomes repressed spontaneously. Genomancers can repress their own expressed mutations at will using the Attunement skill, and they can do it on other beings using the Genetic Knockout Edge.
Aberrations are also considered mutations, so they can also be in a repressed state, and they can become repressed too.