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. And as we'll see in just a moment, this is known as a frame shift mutation. So let's begin by looking at our DNA antisense strand that is used during the process of transcription. So let's suppose this is our DNA strand.