Which term describes the situation in which two genes express both traits equally in the phenotype?

The term that describes the situation in which two genes express both traits equally in the phenotype is codominance. In codominance, neither allele is dominant over the other, and as a result, both traits are fully expressed and visible in the organism's phenotype. A common example of this is seen in certain blood types, where individuals with one allele for A blood type and one for B blood type will have AB blood type, showcasing the characteristics of both parent alleles.

Incomplete dominance, in contrast, involves a scenario where the phenotype is a blend of the two parental traits, rather than distinct expressions of both. Linkage refers to genes that are located close to each other on the same chromosome and tend to be inherited together, and polygenic characters involve multiple genes influencing a single trait, resulting in a continuous range of phenotypes rather than distinct, codominant traits.