* Classic Dominant/Recessive: In a classic dominant/recessive scenario, a single copy of the dominant allele is enough to express the dominant phenotype. The recessive allele is "masked" and doesn't contribute to the phenotype. For example, brown eyes are dominant over blue eyes. Someone with one brown eye allele and one blue eye allele will have brown eyes.
* Codominance: In codominance, both alleles are fully expressed in the phenotype. They don't "mask" each other, but rather both contribute to the final trait. A classic example is blood type: someone with alleles for type A blood and type B blood will have type AB blood.
* Incomplete Dominance: In incomplete dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes. For example, a red flower (RR) and a white flower (WW) will have a pink flower (RW). The red allele is not completely dominant over the white allele.
So, to answer your question directly:
* Codominance is the scenario where both dominant alleles are fully expressed in the phenotype.
* Incomplete Dominance is a bit of a grey area. Both alleles are expressed, but not "fully" in the way that codominance is.
It's important to remember that there are many different types of gene interactions, and the terms "dominant" and "recessive" aren't always black and white.
