An Individual Carries the Allele for Polydactyly, but is Normal

Question

An individual carries the allele for polydactyly, but is normal. This is an example of ________.
A) simple Mendelian inheritance
B) incomplete dominance
C) incomplete penetrance
D) codominance
E) gene dosage

Accepted Answer

Incomplete penetrance is the phenomenon where an individual carries a dominant allele for a particular trait, but does not express that trait. In this case, the individual carries the dominant allele for polydactyly (having extra fingers or toes), but does not exhibit that trait and appears normal. This is different from simple Mendelian inheritance, where dominant traits are always expressed if the allele is present, and from incomplete dominance and codominance, which involve blending or combination of traits. Gene dosage refers to the effect of having different numbers of copies of a gene.