Humans aren’t the only  genetic engineers out there.

I mean, they might not understand  either the concept of genetics or engineering, but plenty of  other life forms can take a gene from the DNA of one organism, and  get it into the DNA of another. Sometimes they even do it on purpose.

But maybe it’s more appropriate for me to call it by its more technical name:  horizontal gene transfer. It’s why bacteria keep becoming resistant to the antibiotics we’re using to kill them. It’s why ferns survived the  literal rise of sun-blocking trees.

And it may be why there’s a fish swimming around in the ocean right now, conjuring  its inner Dr. Frankenstein. [♪ INTRO] Okay first off, let’s  remember what a gene even is. It’s basically a set of instructions  in your DNA, or any creature’s DNA, that tells the body to do a very specific thing.

Like, make this exact protein  that goes on to do that exact job. And many of you might be familiar  with vertical gene transfer, which is when genes are passed down to  the next generation via offspring. This is how genes are typically transferred in plants, fungi, animals,  and yes, even your parents.

But if vertical gene transfer  is like giving your child an index card with grandma’s  recipe for shepherd's pie… then horizontal gene transfer  would be like handing that card to a stranger that  you bumped into on the street. And in prokaryotes– our distant, usually single-celled cousins whose cells don’t have nuclei to house their DNA– it almost is that simple. For example, in a process known as transformation, a prokaryote may just stumble  upon some loose genetic material and incorporate it, pocketing it like  a five dollar bill from the street.

Or in conjugation, two prokaryotes  may do something akin to open mouth kissing, which allows them  to exchange genetic material. And sometimes, that genetic material  is extra good at transferring from one organism to another  because it’s a “jumping gene”. More formally called a transposon.

These genes can actually move around in a cell. Like, just up and take a stroll down the genome to find a new spot for themselves. And because of this mobility,  transposons can mosey right across that open mouth kiss  bridge, and nuzzle into other prokaryotic genomes too.  another prokaryotic genome.

So horizontal gene transfer is easy peasy lemon squeezy for prokaryotes. It’s why antibiotic resistance  is such an issue these days. But that doesn’t mean prokaryotes  have a monopoly on the practice.

Prokaryotes can also transfer genes to eukaryotes, better known as life whose cells have nuclei. The group includes everything  from single-celled amoebas, to you, to your overwatered houseplant. But eukaryotes can also transfer  genes between each other.

Yes, even your overwatered houseplant. Hundreds of millions of years ago, ferns found themselves in a tricky situation. Angiosperms, or flowering  plants, had recently evolved and were popping up all over the place  and blocking out quality sunshine.

So the ferns were faced with a challenge: make do with what little sunshine  they got from the shade, or die. But seemingly out of nowhere, a  gene appeared in their DNA that let them thrive even without a ton of sunshine. It single handedly enabled  ferns to live in the shade.

And once they had this advantageous gene, you can bet they passed it down to their kiddos through regular old vertical gene transfer. But ferns didn’t start with this gene. And given how key it was to their success, researchers wanted to know where it came from.

After analyzing forty plant genomes, the scientists found the shade-thriving gene in one other plant: hornworts. And when they dug a little deeper, they found that the ferns  didn’t just happen to evolve a similar version of the hornworts’ gene. They took a copy for themselves,  roughly 179 million years ago.

This was the first evidence of plant  to plant horizontal gene transfer. But the big question was how it happened. Luckily, the researchers have pretty solid ideas.

See, ferns and hornworts  aren’t like seeding plants, which make little armored seeds and send them on their merry way to break open and grow. Instead, they produce spores,  which inevitably blow off and land in a moist location  to germinate into gametophytes, which then release their own sperm  and/or eggs into nearby puddles. The sperm then swim around until  they find an egg to fertilize, to then grow into a new fern or hornwort.

So it’s a happy little pool of  fern and hornwort sperm and eggs. But like a highschool coed  lock-in, the researchers doubt everyone stayed nice and separated. In fact, this is the place where  the genomes of the hornwort and fern are least defended and  most prone to contact one another.

No cell wall chaperones around. So they hypothesize that one  of these love puddles was the site of a little horizontal  gene transfer between the two. If prokaryotes participate  in horizontal gene transfer through metaphorical kisses, and  ferns did it through slightly less metaphorical love puddles, then some  other plants do it through hugs.

Really, really close hugs. The kind  where you literally fuse together. Now, plants mixing genes together  isn’t really a surprise on its own.

It happens a lot with  hybridization, where the species are close enough relatives to cross pollinate and make baby plants that  feature genes from both parents. But that’s noticeably different  from the hijacking of a single gene like we saw with  the ferns and hornworts. So witnessing a genetic exchange in the absence of cross pollination would be quite the surprise.

But one team of researchers  out of Germany and Poland figured out a way to achieve this:  the aforementioned plant hugs. Okay, they didn’t call them plant hugs. The more appropriate term is grafting.

So they grafted together two  species of tobacco plants: tree tobacco and cigarette tobacco. And to see if the genomes combined, they made sure that the  plants each had a different gene that made them resistant  to a different antibiotic. If the resulting plant and its offspring  were resistant to both antibiotics, then that would be evidence that the genomes did combine via horizontal gene transfer.

And that’s exactly what they found. But plants, you may have noticed, don’t play by the same rules animals do. Because while human genetic  engineers can take a single gene from a spider and put it into a goat’s genome, you can’t sew a spider and goat  together to get a “spoat” genome.

As cool as that would be. So you might think it’s  impossible for one animal species to horizontally transfer a gene  without human intervention. But, surprise!

It’s already happened, thanks to those jumping  genes we discussed earlier. For example, one transposon called  Bovine-B managed to snake its way into certain frog genomes from  their natural predators: snakes. In an article published in the journal  Molecular Biology and Evolution, researchers sequenced the DNA of  several snakes, frogs, and other species to see how the snake  Bovine-B gene was getting into frogs.

And they concluded that  while it may start in snakes, the gene likely didn’t go  directly into their prey. Instead it probably jumped first into something like a parasitic mite, and then into the frogs. That means that not only can  horizontal gene transfer occur in animals, but it can even  occur with a two step process.

From animal to animal vector to animal. And the crazy thing is that unlike most genes, Bovine-B doesn’t even seem  to have any genetic benefit. Rather than being a positive  mutation those first frogs kept around because it helped them survive, scientists think Bovine-B is popular solely because of how good it is  at replicating and jumping.

But if you’re looking for something closer to that fern and hornwort example, we can talk about a jumping  antifreeze protein, or AFP, gene. Antifreeze proteins are  exactly what they sound like: proteins designed to stop ice crystals from forming in the body when it’s super cold. So if you’re a fish who frequents  arctic or antarctic ocean waters, that would be a pretty good gene to have.

That means it isn’t too surprising to hear that both herring and smelts have  this antifreeze protein. But like the fern and the hornwort,  they’re both using the same gene. It’s a clear example of horizontal gene transfer.

And since the herring has eight copies of the gene while the smelt only has one, it’s pretty easy to figure  out who the copycat was here. [Pst] It’s the one with fewer copies. And fish kinda reproduce like ferns, in that they get it on by  releasing all their eggs and sperm into one shared, watery ecosystem. So it’s reasonable to think this AFP gene was horizontally transferred from the herring to the smelt at this point in their life cycle.

Unfortunately, it’s much easier to show that the horizontal gene transfer happened at all, rather than figure out how it happened. And given how rare horizontal  gene transfer appears in life as complex as frogs or fishes,  it can be difficult to set up experiments that can test what’s going on. But that doesn’t mean it’s impossible.

Compared to proverbial hugs and kisses, our last method of horizontal gene  transfer sounds a lot less gentle. Because it involves a literal shock to the system. The method is called electroporation,  and as the name suggests, it involves using electricity  to create tiny pores in a cell.

Those temporary pores can then let materials pass through them, including DNA. So electroporation is a  choice method for scientists who need to do things like add or remove genes from their mice or cell culture test subjects to figure out what exactly certain genes do. But if you think about it,  the combination of stray DNA, developing cells, and electricity  doesn’t only occur in the lab.

In fact, at this point we know that ocean water is full of sperm and egg cells,  ripe for the modifying. Plus, since fish don’t clean  up their scales or waste while swimming around, it’s equally  well equipped with DNA, too. Now, while human mad scientists  aren’t going around shocking the ocean to create a bunch of mutant  animals, you know what might be?

Electric eels. Which for  the record, are as much eels as they are mad scientists. But knowing this, researchers from Japan wanted to see if electric eels could cosplay as genetic engineers.

To test their hypothesis, they  put a bunch of zebrafish larvae into some water, alongside  snippets of DNA that provided a recipe for a specific protein  that glows green under a blacklight. In other words, if the  larvae managed to incorporate the gene into their own  DNA, they’d wind up glowing. Then, the team let their electric  eel feast upon a nearby goldfish.

In trying to shock its prey, the eel  also wound up shocking the larvae. And they found that the electricity  did cause electroporation in the zebrafish larvae, and  compared to the control groups, more of those larvae did wind up glowing green. This means that hypothetically, wild electric eels that are just swimming around, minding their own business and trying to survive, could also be zapping free-floating DNA into unsuspecting ocean critters.

Which is a remarkable feat for organisms who can’t attend grad school or occupy a lab bench. In addition to that research, a  separate scientist from Slovenia took this idea a step further by  suggesting that lightning strikes could also facilitate horizontal gene transfer. Cue Mary Shelley rolling in her grave.

And cue me off to write a sequel to Frankenstein. Where the doctor is a giant sentient  electric eel and he’s, like, making pointless animal  hybrids using his own body. And while I work on that, real scientists can work out the actual practical applications.

Because thanks to horizontal gene transfer, one species' genomic trash or  treasure could easily become… another species' genomic trash or treasure, too. Thanks for watching this episode of SciShow. And an extra special thanks  to our President of Science: McLaren Stanley!

I will definitely not be  emailing you my first draft of Frankenstein 2: The real  modern Prometheus is a giant eel. Because we all value your support too much. [♪ OUTRO]