Genes code for unique polypeptide types in hemoglobin

Steps:

• A gene specifies the amino acid sequence for one type of polypeptide.
• Hemoglobin contains four polypeptide chains: two identical α-globins and two identical β-globins.
• The two α-globins share one gene, as they are identical.
• The two β-globins share another gene, as they are identical, requiring only two genes total.

Why B is correct:

• Each distinct polypeptide type (α and β) requires one gene, per the one gene-one polypeptide definition.

Why the others are wrong:

• A: One gene cannot code for two different polypeptides (α and β).
• C: Four genes would incorrectly assume each chain copy needs a separate gene, ignoring identical sequences.
• D: Eight genes overcounts by doubling the chains without basis in genetic coding.

Final answer: B