 If all we had were those single nucleotide mutations, life would be very boring. We wouldn't have any species evolve or anything, but that's not how nature does it. Remember those domains we talked about in structure, and in particular when we compare this to say natural selection or intelligent design. You don't have say an eye evolving by gradually changing one base at the time and as spontaneously we would get something sensitive to light. What nature does it is that we tend to reuse entire domains. Remember the voltage sensors, the bacterial pH gated ion channel that then had extra domains added to make it voltage gated instead. One of the ways nature does this is so called recombination. A recombination literally means that if I have say a pair of chromosomes or something here, actually it might be better to do it this way. Here I have one chromosome and then here I have another chromosome. If these are now enclosed spatial proximity, what will occasionally happen is that you will exchange parts here. So that actually that's a bit large. So I will have a tiny part here and up there and similar here I would have a tiny part of that chromosome and up there. Do you see how they traded places? That's why in general why we are not identical to our siblings. Partly the recombinations and partly that we have lots of single nucleotide polymorphisms. We know a little bit more about this and there are even enzymes to help this recombinases. So this is an example in the protein data bank of a structure. Do you see here that you have four DNA chains stitched together but they're not so they have blue, red, orange, yellow. So this is one of those transition states where we have the recombinase bound to both these chains and then they're going to cut off two different chains to make the switch over. You can make these switchovers in much more complicated fashions because if we take the top one there we can actually exchange just a very tiny part from one of them to the other. Well I should make that red instead so that we have a tiny part there switched over. And this way I can borrow an entire part of a gene corresponding to say a voltage sensor and insert that in my ion channel that then makes it a voltage-skated ion channel. Now of course the likelihood that this is going to succeed is pretty small but nature has had 4.3 billion years of trial and error and just now and then this works. When these changes are large they will lead to different proteins and we can end up with different proteins in two ways. There are three important words here I need you to learn so let me erase this and I'll do that on the next slide.