An individual who displays the disease sickle-cell anemia must haveinherited the deleterious allele from both phenotypically normalparents. this individual is therefore

a. heterozygous.
b. homozygous recessive.
c. haplozygous.
d. homozygous dominant.

b. homozygous recessive.

Explanation:

The allele for sickle cell is recessive. That is, an individual with the AS genotype is a carrier of the allele but is normal because the A alleleis dominant over the S allele. For an individual to suffer from sickle cell anemia, it is a must that the parents must be carriers of the S allele. Thus the individual has a genotype which is SS which is homozygous recessive.