Sometimes one person with a dominant allele will express a trait, yet that same genotype in another person will remain silent. This is an example of differences in penetrance. 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.