What is the phenomenon where one allele completely masks another called?

The phenomenon where one allele completely masks another is known as complete dominance. In this genetic scenario, if an individual has two different alleles for a gene (one dominant and one recessive), the dominant allele will dictate the phenotype, effectively "hiding" the effect of the recessive allele. This means that the traits associated with the dominant allele will be expressed in the organism, while the traits associated with the recessive allele will not be apparent in the phenotype unless the individual is homozygous for the recessive allele.

For example, in pea plants, if the allele for purple flowers is dominant over the allele for white flowers, a plant with one purple-flower allele and one white-flower allele will have purple flowers. The recessive white-flower trait does not manifest because it is completely masked by the dominant purple-flower allele. This clear pattern of inheritance is fundamental to understanding Mendelian genetics and contributes to predictions about offspring traits based on parental genotypes.