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DNA spells evolution

AP.BIO:
EVO‑1 (EU)
,
EVO‑1.J (LO)
,
EVO‑1.J.1 (EK)
DNA weaves together the tapestry of life on Earth. It mutates, which can lead to variation among organisms. Watch how natural selection relies on DNA to mold organisms to suit their environments. Play the Evolution Lab: http://www.pbs.org/nova/labs/lab/evolution/  .

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  • blobby green style avatar for user anay7529
    At 2 minutes 6 seconds what are double helical threads?
    (3 votes)
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    • duskpin ultimate style avatar for user Elena
      Hello! He is referring to how DNA or genetics connects all living things. "Double helical threads" describe the structure of DNA which is a double stranded helix. Basically a twisted ladder. DNA is made of two backbones made of alternating sugar and phosphate which are connected by nitrogenous bases. Hope this helps!
      (2 votes)
  • hopper cool style avatar for user Grace  McIntyre
    If variation occurs because of a falsely copied base pair in the DNA, wouldn't it mean that eventually, there would be all sorts of combinations, not just adenine with thymine, and cytosine with guanine? It seems like if mutations occur, then the pairs would not match up, causing many wrong base pairs. Or does it eventually fix itself?
    (2 votes)
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  • duskpin ultimate style avatar for user Ayana
    At , is it possible for adenine to pair with guanine or cytosine?
    (1 vote)
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  • blobby green style avatar for user HaileyR
    At ; what are double helical threads?
    (0 votes)
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    • duskpin ultimate style avatar for user Elena
      Hi, Hailey! He is referring to how DNA or genetics connects all living things. "Double helical threads" describe the structure of DNA which is a double stranded helix. Basically a twisted ladder. DNA is made of two backbones made of alternating sugar and phosphate which are connected by nitrogenous bases. Hope this helps!
      (1 vote)

Video transcript

If Darwin came back today, what would he be most excited by in modern science? I think it would be the whole world of genetics. That’s the answer to all the big questions he had – how does variation emerge? And how could that be transmitted? Let’s return to our brown bears stranded in the Arctic to consider the impact of genetics on our understanding of evolution. Each bear is made up of cells. And if we take a brown bear cell, and tunnel into its nucleus, we find DNA – the molecule with the genetic instructions for building, in this case, a brown bear, written in a four-letter code. Now, the thing about DNA—it’s not perfect. When it’s copied, mistakes get made. Mutations, in other words, that sometimes affect an organism’s traits and that sometimes can be passed from parent to offspring. So the variation at the heart of evolution—it’s genetic variation. Slight differences in DNA that—for example—could make some bears a bit lighter in color, a bit more insulated against the cold, and a bit more capable of digesting fattier foods like seals. Evolution is essentially any change in the genetic composition of a population. Mutations are random, so they’re not always helpful. But the bears with mutations that gave them some advantage for Arctic living survived and reproduced more often than bears without them. They passed the genes responsible for those adaptations onto their cubs. Over generations, more bears inherited and elaborated on these and other changes in the DNA. The eventual result – a polar bear. And when we tunnel into its cells, we find polar bear DNA. Think of DNA as the raw material that—across billions of years—evolution has molded and built into countless forms of life. We are all related, tied to one another by the most spectacular of double helical threads.