Medical Genetics Missense mutation Original DNa code for an amino acid sequence DNA→→ CATCATCATCATCATCATCAT bases His h His h His h His H His H His H His h. Amino acid Replacement of a single nucleotide. CAT CATCAT CCT CATCATCAT H HisH HisH His H ProH HisH HisH His Incorrect amino acid, which may produce a malfunctioning proteinMedical Genetics