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DNA spells evolution

AP.BIO:
EVO‑1 (EU)
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EVO‑1.J (LO)
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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?
    (4 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!
      (4 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?
    (4 votes)
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  • leafers tree style avatar for user Inquisitive one
    Isn't it just Natural Selection when the fur of one one bear becomes lighter in shade and color then another? Because that doesn't really give any more support for the evolutionary theory than if some one with brown hair had a child with blond hair. The species doesn't change.
    (1 vote)
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    • male robot hal style avatar for user Charles LaCour
      No, evolution is the change in heritable characteristics of biological populations over successive generations.

      DNA and genes are how heritable characteristics are passed on from one generation to the next.

      Selection both natural and artificial determines which of these inherited changes are beneficial and which are detrimental.

      What you are referring to is speciation, speciation is an effect of the buildup of genetic changes in separate population of the same species to the point where members of the two populations can no longer produce viable offspring.

      Speciation doesn't happen from one generation to the next, it takes many generations for the changes to build up.

      Look at the species okapi and giraffe. They are both decedents of a common ancestor with short necks. For their ancestor a major selection pressure was neck length. Ones with longer necks we better able to get to high branches for food. The longer the neck the more resources it had access to so the ones with long necks were able to stay put where the food was high but ones with a shorter neck either went hungry or found places with lower food. This spit the population which allowed for speciation and we now have shorter necked okapi and long necked giraffe.

      If you look at the DNA and the physical characteristics of okapi and giraffe they are very similar. There are even issues like a nerve the recurrent laryngeal nerve that connects the brain and the larynx. In okapi this nerve branches off the vagus nerve down in the chest, in a giraffe this is the case as well but because of this the nerve has to travers from the brain down into the chest and all the way up to the top of the neck where the larynx is. This design is better explained by progressive elongation of the neck of giraffe over time than it being made that way to begin with.
      (5 votes)
  • blobby green style avatar for user HaileyR
    At ; what are double helical threads?
    (1 vote)
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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!
      (3 votes)
  • duskpin ultimate style avatar for user Ayana
    At , is it possible for adenine to pair with guanine or cytosine?
    (2 votes)
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  • blobby green style avatar for user Carrasquel Gabriel
    how long would dna last with it being still fresh
    (1 vote)
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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.