Answer:
Incomplete dominance is a blending of two phenotypes while co-dominance is a simultaneous expression of both phenotypes.
Step-by-step explanation:
Gregor Mendel discovered the principles that governs inheritance and in one of them, he discovered that an allele (a gene variant) has the ability to mask the expression of another allele in a heterozygous state. He called the allele that masks, DOMINANT allele while the allele masked, RECESSIVE allele. However, exceptions to this principle have arose.
Genetic scenario whereby an allele does not completely mask the expression of its pair in a gene, leading to a hybrid that blends the combination of the two phenotypes, forming a third intermediate phenotype different from both parents'. This kind of inheritance is called INCOMPLETE DOMINANCE.
Another case has occured whereby neither of the two alleles is dominant nor recessive over the other. Hence, the two alleles are both expressed in the individual organism making the organism express both phenotypes simultaneously.
The difference between these two genetic scenarios is that, in INCOMPLETE DOMINANCE, the alleles are combined in a way that an intermediate phenotype different from the two parental phenotypes is produced while in CO-DOMINANCE, the alleles are combined in such a way that both phenotypes are expressed in the hybrid individual.
An example of incomplete dominance is the case of red and white flowered peas crossed together to produce an intermediate pink-flowered hybrid. An example of codominance is the ABO blood group system in humans in which neither the A allele nor the B allele is dominant or recessive over the other. Both A and B alleles are expressed.