Lesson 3: DNA's Role in Determining Your Traits
Penetrance is defined as the percentage of individuals carrying a particular allele who also express the particular trait associated with that allele. For example, 95% of people who have the allele for Huntington's disease actually develop the trait (the disease) known as Huntington's. Other genes have alleles with high penetrance as well. An example is the ability to taste the bitter compound PTC. There are two alleles for the PTC gene, taster and non-taster. The taster allele shows almost 100% penetrance. This means that almost everyone who has the taster allele has the trait of being able to taste the compound PTC as bitter.
Many genes have alleles with low penetrance. An example is the HLA gene allele DR4. 20% of people who have the DR4 allele develop rheumatoid arthritis as they age.
