Question

If in a DNA, codons are ATGATGATG and cytosine base is inserted at the beginning, which of the following would be the result?

• A. A non-sense mutation
• B. CA, TGA, TGA, TG
• C. CAT, GAT, GAT, G
• D. C, ATG, ATG, ATG

Answer 1

The correct option is C CAT, GAT, GAT, G

When the mutation in single nucleotide base of a DNA segment introduces a premature stop codon or a nonsense codon in the transcribed mRNA, it is the non-sense mutation. Insertion of cytosine at beginning of changes the first codon from ATG (methionine) to CAT (histidine) which is not a stop codon; option A is wrong. As we know that genetic code is read as continuous, nonoverlapping and commaless triplets; thus the first triplet in the changed sequence will be CAT; not CA or C. This makes options B and D incorrect. The triplet sequence is read as ATG, ATG, ATG in an original segment and as CAT, GAT, GAT, G in the altered one. The correct option is C.