[Felicia:] Hey Cait, I've been thinking more about your red hair. [Caitlin:] You considering joining the club? We could get you some dye, sort you out. No problem. [Felicia:] Nah. But remember, in an earlier video, we talked about the difference between my black hair and your red hair. [Caitlin:] Yup. It's all due to the difference in a single gene, just one single gene of the 20 000 tucked away in our chromosomes. [Felicia:] I know. I found a picture of it. MC1R, want to see? [Caitlin:] Cool! There it is. [Felicia:] How do scientists know that a single base pair change in a single gene can lead to red hair? [Caitlin:] Because we have a map of our genome, all of our genetic material. [Felicia:] You're telling me that we now have a map of the almost two dozen chromosomes that make up our genome? [Caitlin:] Yup. I mean, it took over a dozen years and a huge international effort, but we've sequenced the entire human genome. This whole process was called the Human Genome Project. Having a human genome map has been an incredibly valuable tool for researchers and the public. It's made possible lots of important scientific breakthroughs and has led to all sorts of commercially available DNA-based products. [Felicia:] Ah yes, like the advertisements I see on TV. [Caitlin:] Exactly! [Felicia:] Way back, when you told me that your great-grandmother was a Celtic princess, was that true? Or were you just pulling my leg? Did she have red hair, too? [Caitlin:] Well... You caught me... My ancestors did have red hair, but -- honestly -- no royal blood. [Felicia:] So, wait, before when you said you spit in a tube and had your DNA tested, was that a fib, too? [Caitlin:] Er, well... I know all the science behind it! But no, I've never done it. [Felicia:] I don't even know you right now. [Caitlin:] All right, all right. I'll make it up to you. How do you feel about mummies? [Felicia:] I'm listening... [Caitlin:] Well, in addition to the Human Genome Project, we've been able to learn about our ancestors by isolating and piecing together genomes of ancient humans. [Felicia:] No way. Can we do that? Was I grabbing a snack when that was covered in class? [Caitlin:] Look. We're scientists, we can do anything. In fact, we can study DNA from all sorts of ancient specimens: animals, viruses, even the bacteria that cause the Black Plague. [Felicia:] Ancient DNA, eh? That's got a nice ring to it. [Caitlin:] DNA can tell us so much, not only about our own species and human development, but also about pathogens and the world around us. [Felicia:] If you've ever wondered about how your DNA can tell you about your ancestors, your health, life in general, you've come to the right place. Join us this week on... [Both:] DNA Decoded! [Music] [Felicia:] Before we talk about sequencing the human genome, we should ask: What's a genome? [Caitlin:] Your genome is the complete set of 23 chromosomes that live in the nucleus of our cells. Each chromosome is made up of thousands of genes. [Felicia:] Humans have about, ah, 20 000 genes. We now know the sequence of most of these genes. [Caitlin:] Genes vary in size. They can be as small as a few hundred base pairs -- [Felicia:] -- or as large as 2.4 million base pairs! You may have already heard that genetically, humans are only about two percent different from chimps. [Caitlin:] And that the human genome is 99 percent the same across the entire human race. That's true. But the fraction of a percentage that our genes are different from each other, is what makes each of us unique, whether in terms of hair colour, blood type, or if we have hitchhiker's thumb. [Felicia:] The small variations in the sequence of our DNA is called genetic variation. [Caitlin:] Tiny changes in DNA can have a dramatic impact on the characteristics of an organism. Sometimes these characteristics are easy to see, like my hair colour. Sometimes they're harder to appreciate, like the shape of your red blood cells. [Felicia:] Now that we know the sequence of the human genome, researchers are using this information to figure out which genes are responsible for all the different traits. [Caitlin:] And it's not just researchers who have access to the human genome. Do you have the internet? [Felicia:] Is that a joke? Of course I do. [Caitlin:] Then, you can check it out for yourself. [Felicia:] Wait. It's free? [Caitlin:] Free. [Felicia:] For everyone? [Caitlin:] For everyone! [Felicia:] Thanks, thousands of scientists. So cool!