CRISPR-Cas is a powerful new technology
that is revolutionising biology.
It's like cut and paste for DNA.
Using CRISPR-Cas, (or CRISPR for short)
scientists can delete, tweak
or completely replace the genes of any organism.
And they can do it more cheaply, easily and efficiently than ever before.
Researchers are already trying to use CRISPR
to introduce genes for disease resistance into wheat;
insert malaria blocking genes into mosquitoes;
and remove HIV genes from infected cells in humans.
Scientists didn't design CRISPR themselves.
Instead, they borrowed it from microbes like bacteria and archaea.
These micro-organisms use the CRISPR system as a defense mechanism
against invading parasites like viruses.
It works like this:
When a virus attacks a bacterium, it introduces its own DNA into the cell.
DNA contains the instructions for life.
It's made up of four different chemical units,
which the cell reads like a code.
Some viruses use their DNA to hijack the bacterium's cellular machinery,
and make more copies of themselves.
They eventually burst out of the cell and spread to other bacteria.
But with CRISPR-Cas, the bacterium can fight back!
The Cas part of CRISPR-Cas is an enzyme that works like molecular scissors.
The bacterium uses Cas to cut the invading DNA into two,
disabling the virus.
Next, the bacterium inserts a section of the intruder viral DNA
into a special area of its own genome.
Over time, the bacterium uses this area
to build up a library of 'bad guys'.
It forms a kind of parasite hit list,
so that it can recognise them if they attack again in the future.
The bacterium copies these sequences into related molecules called RNA.
Each RNA guide is combined with a Cas enzyme,
turning the molecular scissors into precise targeted weapons.
Now, when they encounter a piece of DNA inside the cell
that matches the sequence on the guide,
Cas will snip the intruder DNA and disable it.
Before we discovered CRISPR,
we thought that the immune systems of bacteria
were simple crude tools that worked for everything.
But now we know their defences are much more sophisticated.
CRISPR-Cas forms what's known as an adaptive immune system;
much like our own.
With it, the bacteria can form immune 'memories' of invaders,
and respond more quickly and precisely if they attack in the future.
Once they figured out what CRISPR was and how it worked,
scientists realized they could take it out of microbes
and use it as a gene editing tool in any organism.
You take a Cas enzyme, and provide your own RNA guide molecule
which matches the genetic sequence of the gene you want to edit.
If you introduce this into a cell,
Cas will then snip the host's genome in precisely the place you specify.
This ends up disabling the gene.
Scientists have even worked out how to get the cell
to stitch a new gene into the place of the cut one.
Scientists can do these things already with other tools,
but CRISPR just makes things easier, quicker and much more accessible.
At its most basic level, CRISPR allows scientists
to study individual genes,
by seeing what happens when you turn them off.
But using CRISPR to accurately edit the genomes of plants, microbes,
animals and humans opens up almost endless possibilities.
Selectively killing antibiotic-resistant bacteria;
engineering the body's cells to fight cancer;
even editing pig genes so that we can use their organs
for human transplants.
The precise nature of CRISPR means we could even use it
to eliminate certain genetic diseases in humans.
These kinds of applications are still some way off.
Even though CRISPR is powerful, it can still make mistakes,
sometimes missing its targets, or making unwanted edits.
And there are ethical concerns about
what should and shouldn't be allowed with this kind of technology,
especially when it comes to modifying the human genome.
CRISPR has come a long way since its origins in tiny microbes,
but it really does have the potential to change the world.
The CRISPR revolution is well and truly here,
and it's only just beginning.