Amino Acid Substitution Defining Hemoglobin C

Steps:

• Recall that Hemoglobin C arises from a point mutation in the beta-globin gene (HBB).
• The mutation causes a specific amino acid replacement in the beta chain sequence.
• Compare options to known substitutions for hemoglobin variants.
• Match the defining change for HbC to the correct choice.

Why C is correct:

• Hemoglobin C results from a GAG to AAG codon change at beta-73, substituting proline with lysine, altering protein stability per genetic mutation definitions.

Why the others are wrong:

• A: Histidine to leucine occurs in HbM Milwaukee, not HbC.
• B: Glutamine to threonine is unrelated to HbC; seen in other variants like HbHoshida.
• D: Leucine to phenylalanine defines Hb Philly, not HbC.

Final answer: C