Penetrance and expressivity

Penetrance and expressivity. This pedigree shows the transmission of camptodactyly in a family with both variable penetrance and variable expressivity. Fully shaded symbols indicate members with two affected hands. Those with affected left hands are indicated by shading in the left half of the symbol, and those affected only in the right hand have the right half of the symbol shaded. Symbols with light shading indicate unaffected family members. There is no penetrance in individual III-4 even though he passed the gene for camptodactyly to all of his children. Variable expressivity includes several phenotypes, including no phenotypic expression, expression in one hand, and one individual (IV-8) with both hands affected.