What is the effect of a frame-shift mutation?

A frame-shift mutation occurs when there is an insertion or deletion of one or more nucleotides in a DNA sequence that is not a multiple of three. Since the genetic code is read in triplets (codons), this shift alters the reading frame of the sequence. As a result, every codon downstream of the mutation will be misread, leading to a completely different sequence of amino acids being produced. This dramatic change can significantly affect the resulting protein, potentially leading to a nonfunctional protein or one with a completely altered function.

The impact of a frame-shift mutation is profound, often resulting in premature stop codons, longer or shorter proteins, or proteins with entirely different properties than originally intended. This is why the option that states the mutation completely changes the downstream amino acid sequence is correct, highlighting the extensive ramifications such a mutation may have on gene expression and protein synthesis.