If you sequenced the DNA of all your classmates, you would probably observe that the percentage of Neanderthal genes in their genomes varies from 0–4%. How would you know whether there is a significant difference in percentage between students with blue eyes and students with brown eyes?

Video transcript

Hi everyone. Welcome back. Let's look at our next question. It says when the Neanderthals became extinct, the percentage of Neanderthal DNA diminished over time but 1.41-4% remains in the genome of modern humans. If neanderthals are currently not existing, why do modern humans still have a little DNA from neanderthals? So we'll think about that. Um We have Neanderthal DNA in our genomes because currently scientists believed that there was interbreeding between neanderthals and modern humans when the populations encountered each other. But neanderthals being extinct, there's no new infusion of Neanderthal DNA into the DNA of modern humans. So over time as humans, modern humans with lower percentage of Neanderthal DNA to interbreed with each other. You'd expect to see that Neanderthal DNA decreasing over time as we do see. But again there's still a small percent that remains even though the neanderthals have been extinct for so long. So let's look at our answer choices and see what would be the best explanation choice A says because it cannot be erased. Well this erased is kind of a confusing word. Um You don't really think of DNA as being erased but how that would be is if it's not passed on to further generations. Well this isn't our correct answer because it absolutely can be not passed on to further generations. Whether you have mutations crossing over events or just the fact that you keep on to have generation of generation of generation of humans with lower and lower percent of Neanderthal DNA interbreeding with each other. So that's not a correct explanation choice B says it is resistant to natural selection? Well this is not our answer? Natural selection absolutely acts on D. N. A. Um When a gene gives an advantage gives greater fitness to the individual that has it, that gene will be more likely to be passed on to the next generation. So if this Neanderthal DNA remains in the human genome, it must give some sort of benefit some added fitness to the individuals such that it keeps getting passed on and keeps getting preserved. So that leads us to choice. See it is still useful for modern humans. And this will be our answer because that would be the explanation for why natural selection has kept on selecting for that small amount of tall DNA that those genes keep getting passed on. They must convey some sort of greater fitness to the individuals that have those genes. Um And there is an example of this is actually the B. N. C. Two gene um which actually causes freckle ng in Europeans uh seems to convey some sort of benefit. Um Scientists theorize that maybe helped them adapt to northern climates. We don't know exactly how, but it seems to be a gene that has been preserved from neanderthals and gave some sort of advantage to european populations and thus has been preserved all this time. Choice D says it cannot be subjected to mutation. Well that is not correct Neanderthal DNA just like modern human DNA can mutate and does over time. So we see if neanderthals are currently not existing. Why do modern humans still have a little DNA from neanderthals? Because choice see it is still useful for modern humans. See you in the next video.