An autosomal recessive disease caused by a point mutation in a gene coding for one of the polypeptide chains of the hemoglobin protein is known as what?

• A. Dominant
• B. Sickle cell disease
• C. Co-dominant
• D. Particulate inheritance

Answer: (B)

This question is testing your ability to connect a specific genetic change to an inherited blood disorder. The sickle cell disease results from a point mutation in the beta-globin gene, which codes for one of the polypeptide chains of hemoglobin. That single nucleotide change substitutes one amino acid in the hemoglobin protein (glutamic acid to valine at position 6). Under low oxygen, the abnormal hemoglobin polymerizes, causing red blood cells to distort into a sickle shape, leading to the clinical problems of the disease.

The inheritance pattern is autosomal recessive, meaning you need two copies of the mutant gene to manifest the full disease. People with only one mutant allele are typically carriers with little to no symptoms. This distinguishes it from dominant inheritance (where one copy causes disease) and from codominant patterns (where both alleles would show effects in heterozygotes). It also isn’t described by particulate inheritance. So the best fit is sickle cell disease, a classic autosomal recessive condition caused by a point mutation in the hemoglobin gene.