Penetrance can be difficult to determine reliably, even for genetic diseases that are caused by a single polymorphic allele.

The second diagram assumes Elizabeth has only a single allele for operancy.

Genetic analysis has shown that luminescence is controlled by a single dominant allele.

Suppose an organism has a single allele which allows it to utilize a particular food.

Genetic disorders are diseases that are caused by a single allele of a gene and are inherited in families.

However, the majority of the mutants were apparently unique with only single mutant alleles isolated.

Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells.

Usually it is a single allele making a single enzyme which can make both A and B antigens.

Many genes are not polymorphic, meaning that only a single allele is present in the population: the gene is then said to be fixed.

Paramutation can result in a single allele of a gene controlling a spectrum of phenotypes.