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Which of the changes below following the start codon in an mRNA would most likely have the greatest deleterious effect?

Which of the changes below following the start codon in an mRNA would most likely have the greatest deleterious effect? Correct Answer a deletion of a single nucleotide

A. A deletion or an addition of a nucleotide in a DNA strand that codes for mRNA produces a frameshift mutation. As a result, the first nucleotide in every codon will become the second, the second nucleotide will become the third, and the third nucleotide will become the first nucleotide of the next codon. Such an arrangement is likely to change many of the amino acids in the sequence (depending upon where in the sequence the frameshift begins) and, thus, considerably affect the final sequence of the polypeptide. Answer choice D may have no effect at all because a change in the third position of a codon will often code for the same amino acid. (This results from the "wobble" of the third position of the tRNA anticodon.) Answer choice B will result in a missing amino acid, while answer choice C will change one amino acid to a different amino acid. These changes may alter the effectiveness of the polypeptide, but not as severely as changing many amino acids, as would occur in answer choice A. The inherited disorder sickle-cell anemia is caused by the replacement of one amino acid by another in two chains of the hemoglobin protein, severely reducing the effectiveness of hemoglobin in carrying oxygen. However, a frameshift in the mRNA coding for hemoglobin would certainly make it entirely ineffective.

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