Answer:
A) a deletion of a single nucleotide would most likely have the greatest deleterious effect.
Step-by-step explanation:
The genetic code in the mRNA is read in groups of three nucleotides called codons, which correspond to a specific amino acid. A change in any of the nucleotides in a codon can cause a change in the amino acid that it codes for, which can affect the structure and function of the protein that is synthesized. The start codon is the first codon read by the ribosome and initiates translation, so it's essential for the correct initiation of protein synthesis.
A deletion of a single nucleotide would disrupt the reading frame of the mRNA, causing a frameshift mutation, and all the codons downstream of the deletion would be shifted by one nucleotide, leading to a different amino acid sequence than the original one. This would likely have a greater deleterious effect on the protein's structure and function than a single nucleotide substitution.
A deletion of a nucleotide triplet would have similar effect as a deletion of a single nucleotide, since it would also disrupt the reading frame. A single nucleotide substitution at the first codon position would change the amino acid at the start of the protein, but it may not be as disruptive as a frameshift mutation. A single nucleotide substitution at the third codon position may also cause a change in the amino acid, but it is less likely to have a significant effect on the protein's structure and function than a frameshift mutation.