Final answer:
A frameshift mutation generally has a more significant impact on the gene product than a substitution mutation, because it alters the entire amino acid sequence beyond the point of mutation, potentially changing the structure and function of the protein dramatically.
Step-by-step explanation:
The impact of a mutation on a gene product depends on the type of mutation and where it occurs in the DNA sequence. A frameshift mutation, which alters the reading frame of the genetic code, typically has a more significant effect on the gene product than a substitution mutation. This is because frameshift mutations lead to a completely different sequence of amino acids from the point of mutation onwards, which can drastically change the structure and function of the resulting protein. In contrast, a substitution might only affect the incorporation of a single amino acid, which might not alter the protein's function if it doesn't impact a critical region of the protein or if the substituted amino acid has similar properties to the original.
For instance, a mutation that results in the replacement of cytosine with adenine in a DNA sequence can lead to a different amino acid in the corresponding position within the protein, which can have varying effects depending on the specific amino acids involved and their roles in protein structure and function. If the substitution leads to an amino acid change in a critical part of the protein, such as a key structural domain or an active site, the impact on the protein's function could be substantial.