An individual who displays the disease sickle-cell anemia must have inherited the deleterious allele from both phenotypically normal parents. This individual is therefore:

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An individual displaying the disease sickle-cell anemia must have inherited the deleterious allele from both parents, meaning they must be homozygous recessive for the gene that codes for hemoglobin. They do not have a dominant allele to mask the expression of the recessive allele. Choice (A) is incorrect because homozygous dominant individuals would not display the disease. Choice (C) is incorrect because heterozygous individuals are carriers of the sickle-cell allele but do not display the disease. Choice (D) is not a valid term in genetics.

An Individual Who Displays the Disease Sickle-Cell Anemia Must Have