Final answer:
In a heterozygous genotype where the dominant and recessive alleles blend to create an intermediate phenotype, the trait shows incomplete dominance, not codominance, complete dominance, or epistasis.
Step-by-step explanation:
If in a heterozygous genotype, the dominant and recessive alleles BLEND or MIX together, resulting in an intermediate phenotype, then that trait is exhibiting incomplete dominance. This is distinct from codominance, where both alleles are simultaneously expressed without blending, creating a phenotype where both traits are fully and separately visible. In contrast, complete dominance occurs when one allele completely masks the other, and epistasis involves the interaction of different gene loci where one gene masks or modifies the effect of another gene locus.
An example of incomplete dominance can be seen in the color of snapdragon flowers, where a cross between red-flowered (RR) and white-flowered (rr) parents results in pink-flowered offspring (Rr). This is because the red and white alleles blend to produce the intermediate pink color. On the other hand, an example of codominance is the MN blood groups in humans, or the ABO blood system, where both alleles are fully expressed.