Question

If there are $999$ bases in an RNA that codes for a protein with $333$ amino acids, and the base at position $901$ is deleted such that the length of the RNA becomes $998$ bases, how many codons will be altered?

• A. $1$
• B. $11$
• C. $33$
• D. $333$

Answer 1

The correct option is C $33$

Frameshift mutation

• Deletion or addition of a single nucleotide causes the frameshift mutation.
• This not only affects the codon containing the deletion/ addition, rather all the codons lying downstream to it.

Number of codons altered

• All the amino acids after the point of mutation is altered.
• Here, the amino acids upto 900th base are not altered.
• Since, three nitrogenous bases form a codon encoding an amino acid, hence, 300 amino acids are normal.
• Therefore, the remaining 33 amino acids [codons] will be altered due to deletion of the 901st base.

Final answer
$b.33$