Albinism in humans occurs when both alleles at a locus produce defective enzymes in the biochemical pathway leading to melanin. Given that heterozygotes are normally pigmented, which of the following statements is/are correct?
a. One normal allele produces as much melanin as two normal alleles.
b. Each defective allele produces a little bit of melanin.
c. Two normal alleles are needed for normal melanin production.
d. The two alleles are codominant.
e. The amount of sunlight will not affect skin color of heterozygotes.