This is Cinders. Her ancestor and mine diverged about twenty million years ago. She's not my closest primate ancestor, that's the chimpanzee. And the chimpanzee is so close to us it was only five million years ago that we diverged that the DNA their DNA and ours our only two percent different. And there they are, this is now the chimpanzee scrolling along below and the human scrolling along above, and in a moment these are all reddish, and in a moment you may see a black one and that's how frequent the difference is. There's the first one going by. So you can see the chimpanzees and us share almost the same DNA code. And we originated in Africa. That's where we left out primate cousins behind and we walked out from the top of Africa there; we walked across all the world. And as we went, our DNA changed. And that's how we accumulated these two- percent variation compared with the chimpanzees.

But how exactly did those differences arise? Oh, she doesn't like to go. Yeah. Yeah. Yeah. It takes a thousand years, if you were to write it out about to make new copies. It doesn't take us anything like that long obviously. We have enzymes that copy it at the rate of fifty bases a second and the accuracy is very good indeed. Again, if you were to do a spelling test and copy it out then you would find that you made quite a lot of mistakes. But the enzymes make very very few mistakes. In fact they can make as little as one mistake in the whole of the genome as it is copied. But nevertheless errors do arise, and that's why we've become different from Cinders, and that's how we become different from each other. And the mistakes arise because of radiation, cosmic radiation coming in all the time, radiation in our bodies, chemical changes in the DNA. So we're constantly corrupted. And this is the raw material of evolution. And it's what leads us to have a unique edition of the genome, each one of us.

If the differences are harmful, then of course they get eliminated by natural selection as we've heard before. But if they're neutral or if they're possibly going to be useful, we can't tell the difference usually at first, then they will persist, and accumulate in the population, so that between any two copies of the human genome in this room there are just one in a thousand differences roughly. It's important that the differences get mixed from generation to generation. Think what happens when a parent or couple of parents are going to make a child. This is the father here, and he's going to make sperm, which will fertilise the egg from the mother, but before he makes the sperm, his pairs of chromosomes re-combine like that. This is just one of the twenty-three pairs of chromosomes that he has and they re-combine one of the pair is lost and the other is given to the child. The child, of course, needs two of these chromosomes. The mother is doing the same thing, and she re-combines her chromosomes and gives one to the child and the other is lost. You notice that the re-combination happens at different levels. And this happens again throughout all the twenty- three chromosomes so the child gets a unique set of chromosomes that's not shared by anybody else. The variations have accumulated in the genes and each pair of genes on here will have two different varieties. Usually there will be a difference between the gene on this chromosome and the gene on that, and we call those different varieties alleles. The different versions of the gene. But you can see that because of the clipping the cutting at every generation the combinations of those variations gets scrambled. And so we talk about the gene pool in the population. If the same parents make another child exactly the same thing will happen. I've already done the cut here and here is child two, and you can see that it's different again. So that each child of those parents will have a different set of combinations of the genetic variants that are present in the original parents.

Let's try looking at a feature of you to see how genes are inherited. Look at your neighbour's earlobes please. And see or tell your neighbour whether they have dangly earlobes like me, that are separated from their head, or whether they join straight across, are attached earlobes. Have a look now. OK. Have you done that? Now can everybody who has dangly earlobes put your hand up. That's most, the majority of people. Put those down. How many have attached earlobes, straight across. Fewer. Now the reason is that the attached earlobes are caused by an allele pair of genes and you have to have those particular alleles on both of that pair of chromosomes. You have to have the same allele. We call this recessive. This is what gives rise to the attached earlobes. If you have just one of the other alleles or if they're both of the dangly kind, then you'll be dangly. That's the dominant gene. So you can see something coming down in a very clear genetic way.

But now let's look at something more complicated and we'll look at an actual gene which people have been studying which influences very strongly hair colour. Let's have a look at that gene. This is the gene MC1R. And we have three visitors here who have varieties of hair who are coming down now which will allow you to see how it all works. The sequencing machine's been running a sample of course and that's where this sequence comes from, because we've been running their three DNAs. We've pulled them out by PCR which is a process that amplifies particular chosen segments of DNA and allows us to see them, and those samples have been sequenced and put through here and then we've laid out the results on these placards so that you can see them. And you can see that their hair colours are all different. Now this one scroll that you saw flying down in a rather dramatic way which just helps you to see the length of it. It's not a very big human gene, but it is one gene. And you can see now I've sort of scrunched it up in a certain way that there are three places on that that are marked in red, and the reason for marking them in red is that they're the same three places that are shown a bit enlarged on each of these placards, OK. So this one here near me on Alex's is this one. Then you have that one, and then you have the one down the end, then the same for Karen and the same for Yvonne. OK. Now, at the moment, we've got two strips of sequence on that scroll and that corresponds to the two chromosomes containing this gene, the two copies of the gene in what we call the wild type. The most common one in this room, all the people with darker hair are likely to have more or less that same sequence. Particularly in these three critical sites. Now, we're going to ask our visitors to flip over to show you what changes they have if any in critical places. And there we are, Carol has flipped over, Alex has, Yvonne has not because she with her dark hair is wild type. Wild type just means more common. It doesn't mean she's wilder. OK. So she has the same as is on the sequence, again you see the placards show the two copies, the two chromosomes that correspond to her inheritance from her two parents. What about you. You've got just one change on one of the copies. So one of these three critical places there is a base change here you see how it's gone from G to C. That's another allele and the effects of that allele is to reduce the function of this gene a bit so Karen's hair is fair. It's not as dark as Yvonne's it's fairer. But now over here you can see that in another critical place over here both these C's have been turned into T. So that Alex, he has lost the function of both copies of the gene very considerably and the effect of that is to leave the sort of recessive character, the hidden character of red hair. And so that's how this particular gene works.

There are many other sorts of alleles floating around in the population. It's important to notice there are two copies for each person, but there are many more varieties of the gene, many more alleles for the gene than that. And you can have combinations of these things, so that another person might have a change here, and change over there and red hair for that reason you see. So it's a combination of changes that reduce the function of the gene, which convert the strong brown hair colour down to the red. OK, well thank you very much, that's terrific.