How Much Junk Is in Your DNA Trunk?


once a year or so a study makes the rounds that supposedly ends the idea of junk DNA like we thought most of our genome was garbage but this time we’re sure that it’s not see it the human genome is 3.2 billion base pairs long and contains around 20,000 genes stretches of DNA that code for protein but those genes only make up about one to two percent of our DNA the other 99% of our genome is non-coding and the question of whether it’s useless or not has been hotly debated by biologists since the term junk DNA was coined in the 1960s so is there really a bunch of DNA that doesn’t do much of anything or does it all do something and we just haven’t figured out what it seems like our genomes shouldn’t be mostly junk it takes energy to copy and maintain large amounts of DNA so it seems like we should get rid of any extra baggage and well it’s pretty easy for biologists to say that coding DNA does something it’s tricky to make the call about different types of non-coding DNA protein coding DNA has a clear and elegant function a stretch of DNA is transcribed to RNA and a cell’s nucleus and then translated into a protein proteins do things that you can pretty easily study like helping with chemical reactions are building a cellular structure and humans are made up of thousands of types of cells which each need different kinds and amounts of proteins to do their jobs so every cell needs a way of handing out instructions for how much to make of what stuff enter transcription factors proteins that increase or decrease the chance that a gene will be transcribed into RNA they can be switched on in response to all kinds of things like chemical signals from outside the cell or a certain stage in the organisms development and this is where a couple important types of non-coding DNA come into play with a clear purpose transcription factors bind to DNA but not directly to genes instead they bind to stretches of DNA that don’t code for anything but have a direct effect on genes for instance promoters are right in front of genes there where the machinery that transcribes RNA actually comes together and gets to work when a transcription factor binds to a promoter it helps everything get going now naming all of the different kinds of non-coding DNA and what they do would be a little much but let’s talk about a couple you might have heard of before like there are introns gaps in coding regions that seem kind of like junk but actually a cell can cut them out to mix and match segments of coding regions and create variants of a protein from a single gene there are also bits of non-coding DNA that get transcribed into RNA that never gets translated into a protein collectively called non-coding RNAs the structures that directly assemble proteins called ribosomes are partially made up of non-coding rnas and transfer RNAs shuttle around the building blocks of proteins some others like micro RNAs and long non-coding rnas act more like transcription factors they change the expression of a certain gene or region of the genome in indirect ways so molecular biologists are interested in studying things like all the nitty-gritty functions of transcription factor binding sites and non-coding RNAs and by some definitions any DNA that binds to a transcription factor or gets transcribed into RNA is considered functional which seems like a victory for the anti junk way of thinking this idea peaked in 2012 thanks to the publication of a lot of research by an international consortium known as encode it’s short for encyclopedia of DNA elements they made a remarkable claim that 80% of the human genome is functional in some way encode used a variety of molecular biology techniques to support this idea most of them had something to do with whether a transcription factor binds to a given piece of DNA for example chips seek is a way to isolate segments of DNA where a particular transcription factor binds which scientists can then sequence the idea behind encode is really cool it was meant to help anyone who wanted to study specific stretches of DNA like a database of what binds there and what non-coding RNAs are produced but there was immediate push back against that 80% of the human genome is functional idea it wasn’t that encodes research was bad this was a huge international group of reputable scientists their definition of functional was just way too generous as even some of the authors admit it’s like great you found places where transcription factors stick to DNA but some regions of DNA can be kind of sticky certain proteins might tend to bind there purely by chance and that doesn’t necessarily mean anything is happening there other than stickiness that’s only one criticism of many but you get the idea saying 80% of our genome is functional is probably too generous now different fields of biology work with different scientific tools molecular biologists research very small biochemical reactions and the like as their name suggests meanwhile evolutionary biologists are studying genome function through a broader lens like trying to figure out why different organisms have vastly different genome sizes for instance onions and African lungfish have way more DNA than humans do meanwhile tougher fish seem to have weirdly little no one’s complaining that humans are better than onions and that they somehow deserve to have more DNA it’s just that being a human and being an onion are two very different things and it shouldn’t take five times more DNA to be an onion even if they are very tasty and have all those layers like ogres the simplest answer to this puzzle is that a lot of DNA just isn’t doing anything it’s junk even though maintaining extra DNA might be a little more energetically costly the process of natural selection might not stop it from piling up unless it seriously affects survival and turns out having extra DNA could also maybe help in some cases consider pseudogenes which led to the coining of the term junk DNA pseudo genes are what happened when a gene gets duplicated initially both copies probably work if one of them picks up a beneficial mutation tada you got a brand new gene thanks evolution but if one picks up a detrimental mutation the duplicated gene stops working while the original chugs on normally the messed up version doesn’t get pruned from the genome though it hangs around as a non-functional bit of DNA that still mostly looks like a gene hence pseudo gene a junky left over our genome is also littered with viral sequences from old infections loss there are transposons which encode proteins that let that segment of DNA cut itself out of the genome and squeeze in somewhere else that’s all they seem to do they just jump around because they listen to House of Pain too much every now and then a paper assigns a function to some viral gene or transposon but those seem to be in the vast minority and there are a handful of other types of junk that don’t seem to do anything for us it’s hard to estimate how much of the genome is non-functional because these elements are pretty repetitive repetition tends to throw off our sequencing methods because those methods rely on looking at a bunch of copies of the genome at once it’s like throwing 600 copies of Hamlet into a blender the unique parts like alas poor Yorick they’re fairly easy to spot but how many times does Shakespeare use the word the’ if you just get a the you don’t know where to put it overall a lot of the data in support of junk DNA comes from population genetics which involves a lot of math big one paper published in 2017 in the journal genome biology and evolution instead of looking at where transcription factors bind their definition of functional hinged on whether a DNA sequence could be acted on by natural selection in a positive or negative way most mutations that are subject to natural selection are bad because they break some cellular system and make survival less likely the study’s author estimated their rates that harmful mutations build up in humans compared to our rate of reproduction and effective population size that’s a statistical term that refers to how much of the population is finding mates and making babies basically natural selection can only eliminate harmful mutations as fast as a species can breed or they would slowly die out but mutations in junky regions wouldn’t have bad consequences so they would stick around this paper tried to calculate what it would take to maintain a human genome that’s 80 percent functional even using a conservative estimate of mutation rate it concluded that every human couple would have to have 15 children 13 of which would survive and have children of their own which is super unrealistic an earlier paper published by UK researchers in 2014 in PLoS genetics used a similar definition of functional they compared the rates of change of mammalian genomes to one another genes come and go across evolutionary time but by comparing related groups side-by-side researchers can figure out the most important regions a subject natural selection they found that protein coding genes and certain non-coding elements were pretty stable for example promoters were less stable than coding regions but mostly stayed put but other non-coding stretches like transposons weren’t really preserved across species and therefore they might not do much interestingly both of these studies independently came up with similar estimates for how much of the genome is functional the 2017 studies suggested the absolute upper limit for how much of the genome has a function is around 25% but favored a more conservative figure of 10 to 15% in the 2014 study landed at 8.2 percent that’s obviously way less than encodes sweeping 80 percent claim and those estimates still leave room for functional non-coding elements on top of the coding stuff so we still don’t have a clear answer for what’s junk DNA and what’s not because how scientists define functional varies a lot and we’re still trying to understand everything our genomes can do there’s a lot of complexity and those 3.2 billion base pairs and we’d be foolish to think we know every trick but it’s also foolish to think that evolution is so elegant that there’s barely any room for messiness evolution has no end goal and no sense of aesthetics it’s a whole lot of probability so sometimes stuff piles up like DNA that doesn’t do anything in the end we may have to meet in the middle ground to reconcile both of those ideas and of course keep learning thank you for watching this episode of scishow I thought it was really good I liked it if you want to learn more about DNA and really all kinds of science you can go to youtube.com/scishow to subscribe there is also I think a little button right under this video

100 thoughts on “How Much Junk Is in Your DNA Trunk?”

  1. Serious question… how can 3.2 billion base pairs exist in light of concepts like kinetics, entropy and free energy? I've heard cosmic radiation theorized, but I thought gamma rays destroy DNA instead of building it.

  2. what part of my DNA is worth saving? mostly junk but maybe useful junk? I past my DNA along and the new versions were all better than the original, I stand in Awesome appreciation, thanks for this excellent video , all the molecular science was way over my head..

  3. Does these researches include the fruit-fly-labyrinth experiment?
    I mean the one that lets some fruit-flies to navigate a completely symmetric glass labyrinth (in the form of complete binary tree), then selects only the flies that select the left-(or right)-most way, let them breed, repeat the process with their offspring by selecting only the ones choosing the same direction (left/right) etc… rinse&repeat for sufficient number of generations until the newborn flies only take the same route (ie only left for example).
    Basically proving that behavior & decisions (at least some of them) are also stored in DNA somehow and passed to offspring.
    That "junk"-DNA which might appear unused perhaps codes for such things? Consider that behavior is very hard to associate with particular genes since it's something that a fly (or a man) might do only in particular moment and under particular circumstances – ie might be impossible to observe outside of right environment (which doesn't mean there aren't genes to encode for such behavior) … And that's in case you know what behavior you're looking for in the first place!

    Also, as far as I know our genetic engineering is still rather primitive. Ie we can't exactly cut and glue exact pieces of DNA, right?
    But assuming it was possible to acceptable extend is there experiment that tries to give offspring to … lets say a mice (or a plant … or more realistically perhaps some bacterium with very simple DNA) that has its junk-DNA cut-out? If removing of "junk"-DNA fragment leads to noticable changes it would obviously not be Junk! 🙂

  4. Sure, some parts of the HUMAN genome is junk, but then again: we were not Homo Sapiens all the time. There were several ancestors with unique environmental and micro-macrobiological lives. Ask a microbiologists, how many different genomes of harmful bacteria there are. And then ask, how many had ancestors to them. So, to call DNA junk is not wrong, but its not USELESS. DNA gives us adaption. Weather, diet or new microbiological situations. And thats where MOST of our DNA is replicated all the time: when a Swede moves to Southern China to live, it will take a bit of time and a few bouts of sickness to adapt to those conditions. But he WILL adapt. I'd say only 1-2% of our DNA is junk: remnant of ancient diseases and climates, that are still replicated for…just in case.

  5. Would it not stand to reason, that different cell are coding different sections. My liver shouldn't be making proteins specific to my adrenal gland. So that DNA would be junk DNA to my liver, right? Also, wouldn't extra unused DNA decrease the chance of used DNA being hit my UV and damaging it?

  6. 10:15 when science the method mixes with ''science'' the ideology/belief that is haunted traumas from the times of dominating dogmatic religions suppressing independent inquiries of the nature of the universe

  7. It is an arrogance to say that DNA that does not meet a narrow definition of functional is therefore junk and useless. It is likely that most is beneficial, although it may not be in use at all times.

  8. It's all comes down to scientific materialism, that nothing is real unless it is composed of matter (has mass) or electromagnetism. Heaven forbid that information be conveyed in any other method. If the influence can't be isolated in centrifuges, or spectra, then it must not exist. And so we're stuck in a universe where only 4-5% is something other than dark energy or dark matter. When are we going to learn that mater/energy is only a small portion of everything?

  9. One of my best friends is a molecular biologist studying the proteins within mitochondria. She recently discovered some new ways to cause cancer.

  10. So over 50% of any aircraft is junk then? I profoundly dislike the notion of "junk" DNA. There are redundancies, there is space for evolution, there is a bunch of DNA which might be there to absorb harmful mutations, and a lot we don't know yet. But calling it junk… can we please not.

  11. Nice article but you left out one of the coolest things junk dna can do. It may be a bad copy of another gene and not work now, but as mutations stack in it, it can suddenly become active again and change everything!

  12. Wow… we're less living organisms, and more a old computer hard drive, with Windows pre-installed. Littered with redundant files, planned obsolescence, too many copies, corrupted data, dead or missing executables, fragmentation, old viruses, browser-hijackers, spam and trojans. We're a mess…

  13. Hi guys. Nice video.

    Just a feedback. I had problems with the subtitles. It is appearing something like a “ghost subtitle” behind the captions. I don’t know if it’s a YouTube or my iPad problem.

    Thank you.

  14. I freaking hate the term junk DNA.
    I like to think of it like a clutch of fertile eggs. Lots of potential but not all of it makes chicks. Under the right conditions who knows what bit of "junk" today becomes tomorrow's adaptation.

  15. We need these non-coding, intergenic regions for chromatin structure etc.. Google for example "TAD"s (Topologically associating domain) which forms higher order structures of our DNA/chromatin and thereby controls its activity, stability, accessibility and more. Then we have regions close to the centromers ("center" of the chromosome) and the "ends" of the chromosomes (telomers) which act as some kind of spacer/shield.

  16. As Hank states around min 7, the system is heck-a-random and doesn't really make sense. I've recently studied this from a nanotech perspective, and can relate with this feeling so much.

  17. Maybe Junk DNA is just some type of encrypted genome data! maybe there is a private key to decode all that junk data!
    if we have a useful function for these type of encrypted data in our digital computers then we could have the same beneficial function in a biological system like human body! :/
    The question is if this is true why those data had to be encrypted? are we dealing with a proprietary code?
    like a company designed the human genome and wanted it to lock the DNA code so no one else copy and design a better version of it!

  18. What a disappointment! I had a hope that you'll bring "the switches" that control our genes over the presumed junk DNA

  19. I Don't Understand Why 'Muricans Type Things Like This? There Is No Dot After Each Word So What's The Deal With That?

  20. I suspect that some day in the distant future people will think of the idea of Junk DNA the same way we think about the aether or the idea of fire as an element. The hubris in assuming that since you haven't figured it out yet it must be junk is disheartening, but the irony of obliviously invoking the same fallacious argument as a climate change denier is just delicious.

  21. The fact that an area has a function, doesn´t mean that that function is needed for natural selection. The concept of Junk DNA in the best evidence for the Neutral theory of evolution, which states that most variation (certainly genetic variation) does not depend on Natural selection. It doesn´t mean is useless, junk DNA at least uses space, and that space is already programed to be there. But selectively it does not have value. Meaning we might spend tons of ATP on it, but it doesn´t matter for selective evolution. This evidence tells us that, contrary to what most people think – thanks to Darwin -, Nature is nice and easy with us, the eukariots. After all, we are so few. Bacteria, on the other hand, they are so many, Nature is really tough on them, that why they can´t afford Junk DNA.

  22. Well, the comment section was what I expected. Lots of uneducated people posting their opinions that science has long ago demonstrated are wrong.

  23. Telomeres are junk DNA whose purpose is to simply protect the ends of chromosomes and provide a stable scaffolding up until the end of the cell's Hayflick limit. Basically like the tips of your shoe laces. Technically, it's "functional" according to the latest theory of aging. Perhaps genetically engineering the length of this "useless" DNA could extend our lifespan indefinitely. It would be nice to learn of any experiments in this area from SciShow.

  24. Now that we have reasons to believe DNA can carry memories (through transgenerational epigenetic inheritance), couldn't that be the (or a) function of the so-called "junk DNA"?

  25. It turns out that geneticists are bit ahead of SciShow… the noncoding DNA is regulatory. Think of the noncoding regions like the recipe (like baking time, or stirring until mixed, etc…) and the coding regions are the ingredients. Also introns may have a critical function in shielding coding elements from mutations. If a random transposon or mutation hits what is most likely an intron then protein function is preserved.

  26. Could junk DNA be epigenetic DNA ready to blossom into a new organism? Could it explain the gaps in the fossil record?

  27. According to current data there are some families/subfamilies of transposons that are still moving in the human genome (Alu) not to mention that transposons play a huge role in gene evolution and speciation

  28. “Junk” dna could potentially be genetic potential. Consider that if a species had 100% necessary dna, any changes to it would effect the organism in a major way, and most likely result in an organism that cannot function, making adaptation difficult at the genetic level. With junk dna, a mutation can occur without risking damage to important genes. The junk changes and if it happens to be expressed, either phenotypically or on a cellular level, the organism can essentially test drive the mutation without it inhibiting the formation of already important genes.

  29. Great video! For me, this was the sweet spot in terms of depth and technical details. I hope the Complexely Team makes more videos like this!

  30. Clearly it's the DNA backlog of our evolution … which would explaine why it's shorter or longer then other organisms as humans are some of the newest live forms on Earth's evolutionary list

  31. The mechanism of DNA is very sophisticated. The non coding regions might have a role in controling the molecular machines that work on DNA itself. There might even contain a second code that decide which gene should be avtivated.

  32. If this is true could you use crisper to simply cut it out. Or would that have unforeseen consequences like everything else we do?

  33. My whole body is junk dna. Most of it isn't doing much. And then there are people who don't actually believe science and history …and they're up to even less.

  34. Isn't it obvious? The genes are stowaways.https://gnostradamus.wordpress.com/2018/09/29/why-do-we-have-so-much-junk-dna-because-weve-been-hijacked/Genes duplicate because those who don't get eliminated. That transposing genes jump around is a clue–they want to make it more difficult to get eliminated, if they don't stay in one place.

  35. From where I am from as far as I know back then (some 50 years) those industrial birth rates of ~15 kids, required for a population to be able to maintain some 80% of its genome functionally active, were not that rare to find.
     My core family is small in number, particularly. However, many of my closest relatives are almost right there, near the mentioned rate. In one family, there are 11 cousins. Others have around 8 or 7 kids. Moreover, my father equally grew up in a house of 10 brothers and sisters.

    Knowing of many other families that, back there, were big numbered, too, I wonder how far back this tendency goes on. Also, how this could affect, if at all, the genetic relationship inside the society I live on? Any idea, anyone?

  36. The idea I was going with is DNA is a hoarder; for onions it's like the house full o' papers and junk; for pufferfish their DNA was decluttered and for us, we're at the drawer stage in the kitchen or room stage in the house where there's lots we might need and we've kept. Some of it is the inevitable plastic bag drawer, the old screw jars, the lego box the kids had when they were young, some of it is the copper wiring that could be used to put up the fairy lights in the patio we just have not got round to, or the sound system that's to go with them. I'm really impressed with all the coding analogies; you guys just rock.

  37. What if the purpose of the junk DNA is to cut the damage done to meaningful/coding DNA during multiple replication cycles that happens during aging? Like bubble wrap that keeps the vase safe during transport??

  38. I wonder when or how many times certain plants and animals have evolved, when certain things branched off from each other, and how slowly or quickly they did it, and if that effects the amount of junk DNA they have, if at all. I'd love to hear an answer to those questions and if there's any correlation between the two.

  39. What if some genes just activate during embrional/fetal wathever developement and after that they just stop serving or sthg

  40. I would suggest looking at evolutionary development and genetic switches. I would postulate that much of the "junk" is utilized in various switches. We may have sequenced the entire human genome, but we really don't know every single switch in our genome or what they are specific for. Many switches are only used during embryonic development and once their function is done, they turn off.

  41. A thought has crossed my mind as In sure its crossed many others. Junk ,garbage DNA .why haven't any scientists taken that so called DNA and put it in a pietry dish and cloned it? Wouldn't that be spectacul to see what comes of it? I find it fasinating.

  42. You talk like you're sure you know everything about DNA. Where do things like social memories come from? Junk DNA? How did you know to nurse at birth? Junk DNA? Try thinking like a scientist, assume you don't know everything.

  43. If we're so confident that it's junk, why not cut it out, implant it into a cell and see what happens to the organism?

  44. They say it’s junk Cus they can’t understand it but these bastards at the top know it exactly what it is and know it’s it hold too much potential. That part of the dna was was purposely cloaked centuries ago. Human were very much different than they are now

  45. 08:49 16/07/2019
    What do you think? I think in the near future we will start to see ads like this.
    Send us your DNA Code and we will send by return post a 5mtr spool of your DNA
    This will also come with a free tube of human DNA super glue, as a special offer.
    All you need to do is take a photo of your body part that fell off and feeds it into your cad program. this will generate a G-code slicing layout. Just place this in the slot of your
    3D printer and press go. after a little time of printing, you will now have a brand new nose, or ear, maybe a complete foot. be quick offer ends soon. Malc UK

  46. I think that all DNA is somehow useful. For instance if a virus infects a space in the noncoding region then the purpose is to be there to be infected and save our important genes from being disrupted.

  47. "It [evolution] is a whole lot of probability."
    Let me correct you there, Sir. Evolution is a whole lot of IMprobability. Like, a lot. Like mathematically impossible.

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