DNA codon mutation substitutes Glu for Lys in haemoglobin C Steps:

• Compare normal DNA sequence (CAC GTG CAT GGA TGC TGT GAG) and HbC sequence (CAC GTG CAG GAA TGC TGT), noting differences in codons starting from the third triplet.
• Locate GAG in normal sequence, which codes for Glu per the table.
• Recognize the sequence alteration affects the Glu codon, changing it to one coding for Lys (AAG in standard code, though table lists TTA as an example).
• Verify this matches the known single-point mutation at β-globin position 6 causing Glu to Lys substitution in HbC.

Why A is correct:

• HbC arises from a GAG→AAG mutation, replacing negatively charged Glu with positively charged Lys, altering protein solubility per genetic code rules.

Why the others are wrong:

• B. His codon (e.g., CAT) unchanged; no Leu (CTT etc.) substitution.
• C. Asp (GAT etc.) absent from sequences or mutation site.
• D. Pro (GGA) present but unchanged to Thr (ACT etc.).

Final answer: A