In this lecture, we're going to focus on frameshift mutations. Now, frameshift mutations are a result of insertions or deletions that take place on our DNA molecule. Now let's define what an insertion and what a deletion is. An insertion basically refers to the insertion of a nucleotide base pair or several nucleotide base pairs at some given location on our DNA molecule, while a deletion is the removal of a nucleotide pair or several nucleotide pairs at some given position on our DNA molecule. Now, as we'll see in just a moment, an insertion or a deletion may or may not shift the reading frame of our mRNA molecule. Now, what exactly is the reading frame?