Final answer:
A frameshift mutation occurs when nucleotides are inserted or deleted, altering the reading frame of the genetic code and changing the entire sequence of amino acids that follow.
Step-by-step explanation:
A frameshift mutation occurs when there is a deletion or insertion of one or more nucleotides that isn't divisible by three, which changes the reading frame of the genetic code. A normal sequence of RNA could look like this: AUG-AAU-ACG-GCU, which translates to start-asparagine-threonine-alanine. However, if an A nucleotide is inserted right after the start codon, the sequence would be AUG-AAA-UAC-GGC-U, translating to start-lysine-tyrosine-glycine. The insertion shifts all subsequent codons, changing the entire amino acid sequence past the mutation point. An insertion of three nucleotides can add just one extra amino acid but keep the rest of the protein intact, making it potentially less harmful than the insertion of one or two nucleotides.