All-or-none phenomenon

For an individual, penetrance is an all-or-none phenomenon. Either a particular genotype is expressed or it is not.

The concept of penetrance is often confused with variable expressivity, which is the variation in the type and severity of clinical features of a genetic disorder.

When we talk about penetrance however, the severity of the condition is not important. The only factor that matters is whether or not the condition is expressed at all.

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