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Understanding Cancer Series

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  • Posted: 12/29/2009

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Slide 18


Incomplete Penetrance

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Most hereditary cancer syndromes are inherited in autosomal dominant fashion. In classic Mendelian genetics, if an individual carries a dominant allele, the trait will be expressed (genotype = phenotype). However, if all carriers of a certain dominant allele in a population do not express the trait (same genotypes/different phenotypes), the gene is said to have incomplete penetrance. For example, sometimes one person with a dominant cancer susceptibility allele will express a trait, yet that same genotype in another person will remain silent.

Graphic shows that sometimes even when a dominant allele is inherited, it will express itself in one person, and not express itself in another person.