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? Well, the reading frame is the sequence of nucleotides. It's the sequence of codons that is read by the ribosome during the process of translation when we synthesize our polypeptide chain. So let's take a look at an example of an insertion that causes the shift of our reading frame.