Which of the following describes a recessive allele?

A recessive allele is one that does not produce an observable effect on an organism's phenotype when a dominant allele is also present. In the presence of a dominant allele, the traits associated with the recessive allele are masked, meaning that they are not expressed in the organism's appearance or trait.

For example, if we consider flower color, a dominant allele may produce purple flowers, while a recessive allele may produce white flowers. If an individual has one dominant allele for purple flowers and one recessive allele for white flowers, the dominant purple trait will be exhibited, and the white trait will not be observed. It is only when the individual has two copies of the recessive allele (homozygous recessive) that the white flower trait appears.

This information illustrates why the correct description of a recessive allele highlights its role as being masked by a dominant allele.