What is it called when one allele is not completely dominant over another, resulting in a blended phenotype?

The phenomenon described, where one allele is not completely dominant over another and results in a blended phenotype, is referred to as incomplete dominance. In incomplete dominance, the heterozygous phenotype expresses a mix of the two parental traits rather than showing one trait fully dominating the other.

For instance, if a plant with red flowers is crossed with a plant with white flowers, the offspring might have pink flowers, representing a blend of the two colors rather than one color overpowering the other. This differentiation is crucial for understanding various genetic traits and how they present in offspring.

In contrast, codominance occurs when both alleles in a heterozygous organism are expressed equally, leading to a phenotype that exhibits both traits distinctly, such as in certain blood types. Complete dominance is when one allele completely masks the effect of another, resulting in the dominant trait being fully expressed. Meanwhile, the concept of multiple alleles refers to more than two alleles being present for a particular gene, which can lead to various combinations of traits but does not specifically imply blending as seen in incomplete dominance.