Final answer:
Mutations in the middle bases of an mRNA codon might not affect protein function because of the 'wobble' effect and the redundancy in the genetic code that allows for silent mutations. However, frameshift mutations caused by insertions or deletions not in multiples of three can severely disrupt protein functionality.
Step-by-step explanation:
Mutations in the middle bases of a codon in an mRNA do not always lead to changes that affect the function of the protein because of the redundancy of the genetic code. Because the first two bases of each codon are most significant while the third base often varies, a mutation in the third position might not change which amino acid is incorporated into the protein — a phenomenon known as the 'wobble' effect. This can result in a silent mutation, where the resulting amino acid sequence is unchanged, thus having no impact on the protein's functionality.
Silent mutations are one reason a nucleotide change might not affect the phenotype, as they can occur in a manner that does not alter the final amino acid sequence of a protein. Additionally, if mutations occur in groups of three nucleotides, such as insertions or deletions, they may not cause significant effects since codons are read in triplets and the reading frame remains intact.
However, it's important to note that not all mutations are harmless. Frameshift mutations caused by insertions or deletions not in multiples of three can lead to substantial changes in the protein's structure, often resulting in nonfunctional proteins. Therefore, while some mutations may be benign, others can have severe consequences for protein function.