Question

In a thalassemia (blood disease) prevalent in Southeast Asia, the hemoglobin A polypeptide chain is longer than normal, although the mRNA length is unchanged. The normal HbA polypeptide ends with the sequence: – Lys – Tyr – Arg –(C terminus). The mutant version adds 30 amino acids, ending with: – Lys – Tyr – Arg – Gln – (29 more amino acids) –(C terminus). The causative mutation in the HbA gene is most likely:

A. a transition mutation.

B. a transversion mutation.

C. a nonsense mutation.

D. a frameshift mutation.

E. an insertion mutation

Make sure provide the best explanation about your answer by explaining what the question is asking first and then falsify (provide explanation) each of the choices you did not choose. Ultimately, also provide explanation for for the correct choice. Define any key concepts and terms along the way and make diagrams if necessary to provide the best explanation.

Answer 1

transition mutation: a purine is changed to another purine or a pyrimidine is changed to another pyrimidine, this is a substitution mutation, this will not increase the number of amino acids, but it can change one amino acid.

transversion mutation: purine is changed to pyrimidine, this is a substitution mutation, this will not increase the number of amino acids, but it can change one amino acid.

nonsense mutation- a substitution mutation, which changes a codon to a stop codon, so the size of the protein product decreases.

frameshift mutation- mutations that change the reading frame changes, this can be due to insertion or deletion of nucleotides.

insertion mutation- mutation due to the insertion of nucleotides,this can change the reading frame.

here the number of amino acids changes that is after Arginine 30 amino acids are added, this is due to a mutation in the stop codon, the stop codon is UAA, it is changed to CAA, CAA codon codes for Gln amino acid, due to this mutation, the stop codon has changed to another codon so this is a readthrough mutation.

here U ( uracil ) is changed to cytosine, that is a pyrimidine is changed to another pyrimidine, so this a transition mutation.

so the answer is A) a transition mutation