Final answer:
A frameshift mutation significantly alters the protein coded by a genetic sequence due to the deletion or insertion of nucleotides, disrupting the reading frame and potentially changing or halting protein synthesis.
Step-by-step explanation:
A frameshift mutation almost always results in a significant alteration of the protein coded by the genetic sequence. These mutations occur when there is a deletion or insertion of one or more nucleotides that is not evenly divisible by three, which changes the reading frame of the genetic code. Since proteins are synthesized based on codons—three nucleotides that correspond to a specific amino acid—any insertion or deletion has the potential to shift the grouping of these codons and alter the entire sequence thereafter. This disruption can result in an entirely different protein or even cause the translation to stop prematurely if a stop codon is created by the shift. For example, if we take the RNA sequence AUG-AAU-ACG-GCU which translates to start-asparagine-threonine-alanine, and insert an 'A' after the start codon, the new sequence becomes AUG-AAA-UAC-GGC-U which translates to start-lysine-tyrosine-glycine, demonstrating a radical change.
It's important to note that a frameshift mutation resulting from the insertion of three nucleotides may be less harmful than the insertion of one nucleotide because the former does not affect the reading frame in the same drastic way. Inserting three nucleotides essentially adds one amino acid without shifting the frame, whereas adding or removing a different number of nucleotides disrupts the entire downstream protein coding sequence.