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So this is a talk about gene drives,
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but I'm going to start by
telling you a brief story.
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20 years ago, a biologist
named Anthony James
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got obsessed by the idea
of making mosquitos
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that didn't transmit malaria.
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It was a great idea,
but pretty much a complete failure.
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For one thing, it turned out to be
really hard
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to make a malaria resistant mosquito.
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James managed it, finally,
just a few years ago
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by adding some genes
that make it impossible
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for the malaria gene
to survive inside the mosquito.
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But that just created another problem.
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Now that you've got malaria-resistant
mosquito,
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how do you get it to replace
all the malaria-carrying mosquitos?
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There are a couple options,
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but plan A was basically to breed up
a bunch of the new genetically-engineered mosquotos,
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release them into the wild,
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and hope that they pass on their genes.
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The problem was that you'd
have to release
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literally 10x the number of native
mosquitos to work.
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So in a village with 10,000 mosquitos,
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you release an extra 100,000.
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As you might guess, this was not
a very popular strategy
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with the villagers.
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(Laughter)
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Then, last January, Anthony James
got an email
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from a biologist named
Ethan Bier.
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Bier said that he and his grad student,
Valentino Gantz,
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had stumbled on a tool that could not only
guarentee
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that a particular gene trait
would not be inherited,
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but that it would spread
incredibly quickly.
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If they were right, it would basically
solve the problem
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that he and James had been
working on for 20 years.
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As a test, they engineered
two mosquitos
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to carry the anti-malaria gene
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and also this new tool,
a gene drive,
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which I'll explain in a minute.
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Finally, they set it up so that
any mosquitos
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that had inherited the
anti-malaria gene
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wouldn't have the usual white eyes,
but would instead have red eyes.
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That was pretty much just
for convenience
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so they could tell just at a glance
which was which.
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So they took their two
anti-malarial, red eye mosquitos
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and put them in a box with 30
ordinary white-eyed ones
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and let them breed.
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In two generations,
those had produced 38,000 grandchildren.
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That is not the surprising part.
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This is the surprising part:
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given that you started with just
two red-eyed mosquitos
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and 30 white-eyed ones,
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you expect mostly white-eyed
descendents.
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Instead, when James opened the box,
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all 38,000 mosquitos had red eyes.
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When I asked Ethan Bier
about this moment,
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he became so excited, tht he was
literally shouting into the phone.
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That's because getting only
red-eyed mosquitos
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violates a rule that is the
absolute cornerstone of biology,
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Mendelian genetics.
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I'll keep this quick, but Mendelian genetics
says when a male and female mate,
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their baby inherits half of its
DNA from each parent.
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So if our original mosquito was aa
and our new mosquito is aB,
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where B is the anti-malarial gene,
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the babies should come out
in four permutations:
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aa, aB, aa and Ba.
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Instead, with the new gene drive,
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they all came out aB.
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Biologically, that shouldn't
even be possible.
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So what happened?
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The first thing that happened
was the arrival
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of a gene-editing tool
known as CRISPR in 2012.
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Many of you have probably heard
about CRISPR,
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so I'll just say briefly that CRISPR
is a tool that allows researchers
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to edit genes very precisely,
easily and quickly.
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It does this by harnessing a mechanism
that already existed in bacteria.
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Basically, there's a protein
that acts like a scissors
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and cuts the DNA,
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and there's an RNA molecule
that directs the scissors
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to any point on the genome you want.
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The result is basically a word processor
of genes.
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You can take an entire gene out,
put one in,
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or even edit just a single letter
within a gene.
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And you can do it in nearly any species.
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Okay, remember how I said
that gene drives
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originally had two problems?
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The first is that it was hard
to engineer a mosquito
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to be malaria resistant.
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That's basically gone now,
thanks to CRISPR.
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But the other problem was
logistical.
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How do you get your trait to spread?
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This is where it gets clever.
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A couple years ago, a biologist
at Harvard named Kevin Esvelt
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wondered what would happen
if you made it so that
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CRISPR inserted not only
your new gene,
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but also the machinery
that does the cutting and pasting.
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In other words, what if CRISPR
also copy and pasted itself.
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You'd end up with a perpetual
motion machine for gene editing.
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And that's exactly what happened.
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This CRISPR gene drive
that Esvelt created
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not only guarantees that a trait
will get passed on,
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but if its used in the germline cell,
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it will automatically copy and paste
your new gene
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into both chromosomes of every
single individual.
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It's like a global search and replace,
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or in science terms,
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it makes a heterozygous trait
homozygous.
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So, what does this mean?
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For one thing, it means we have
a very powerful,
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but also somewhat alarming new tool.
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Up until now, the fact that gene drives
didn't work very well
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was actually kind of a relief.
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Normally when we mess around
with an organisms's genes,
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we make that thing less evolutionarily fit.
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So biologists can make all the mutant
fruit flies they want
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without worrying about it.
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If some escape, natural selection
just takes care of it.
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What's remarkable and powerful
and frightening about gene drives
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is that that will no longer be true.
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Assuming that your trait does not
have a big evolutionary handicap,
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like a mosquito that can't fly,
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the CRISPR-based gene drive
will spread the change relentlessly
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until it is in every single individual
in the population.
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Now, it isn't easy to make
a gene drive that works that well,
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but James and Esvelt think
that we can.
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The good news is that this opens
the door to some remarkable things.
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If you put an anti-malarial gene drive
in just 1 percent
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of anopheles mosquitos,
the species that transmits malaria.
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Researchers estimate that it would
spread to the entire population
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in a year.
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So in a year, you could virtually
eliminate malaria.
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In practice, we're still a few years out
from being able to do that,
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but sitll, a 1,000 children a day
die of malaria.
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In a year, that number could be
almost zero.
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The same goes for dengue fever,
chicken genuang (?), yellow fever.
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And it gets better.
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Say you want to get rid
of an invasive species,
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like get Asian Carp out of
The Great Lakes.
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All you have to do is release
a gene drive
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that makes the fish produce
only male offspring.
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In a few generations, there'll be
no females left, no more carp.
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In theory, this means that we
could restore hundreds
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of native species that have been
pushed to the brink.
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Okay, that's the good news,
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this is the bad news.
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Gene drives are so effective,
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that even an accidental release
could change an entire species,
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and often very quickly.
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Anthony James took the precautions.
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He breed his mosquitos in
a bio-containment lab
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and he also used a species
that's not native to the US
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so that even if some did escape,
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they'd just die off,
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there'd be nothing for them
to mate with.
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But it's also true that if
a dozen Asian Carp
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with the all-male gene drive accidentally
got carried from The Great Lakes
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back to Asia,
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they could potentially wipe out
the native Asian Carp population.
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And that's not so unlikely, given
how connected our world is.
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In fact, it's why we have
an invasive species problem.
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And that's fish.
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Things like mosquitos and fruit flies,
there's literally no way to contain them.
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They cross borders and oceans
all the time.