Elsevier

Genetics in Medicine

Volume 5, Issue 5, September–October 2003, Pages 347-352
Genetics in Medicine

Review
Penetrance and expressivity in the molecular age

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Abstract

Penetrance and expressivity have been defined through clinical experience. Although penetrance is often seen as the end of the spectrum of expressivity, penetrance and expressivity are considered as distinct phenomena. A review of the known mechanisms underlying either penetrance or expressivity reveals that in most of the cases the same explanation is true for both phenomena. Some of the known mechanisms include modifier genes, the influence of the allele in trans, sex, and environmental factors. Although rapid progress has been made in understanding of the basis of incomplete penetrance and the differences of expressivity, they still remain unknown for most of the genetic disorders. In recent years, it has become evident that there is much in common between the classical Mendelian traits in which the inheritance has been seen as “simple” and most of the common diseases in which the inheritance is “complex.” In both cases genetic and/or environmental factors are acting in a complex way.

Keywords

penetrance
expressivity
monogenic
Mendelian inheritance

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