The researchers took a gene from glowing jellyfish and inserted it into the unfertilized eggs of house cats.

It was a neat trick, but they had a bigger goal in mind.

They also made the cats more likely to be resistant to a feline form of AIDS, by, again, manipulating their DNA.

And cats aren't that different than humans.

In fact, we share around 90% of our DNA with them.

So why can't we engineer humans in the same way?

Well, we can—engineer ourselves to be resistant to life-threatening illnesses, that is.

In fact, one scientist claims that he's genetically engineered two babies using a revolutionary tool called CRISPR.

But what exactly is a CRISPR baby, anyway?

Would you like to be 6 feet tall or never bald?

The secret to traits like these lies in the 6 billion letters of your genetic code.

But there could be something else in there as well: mutations.

Genetic mutations are linked to at least 6,000 medical conditions from sickle cell anemia to Huntington's disease.

But what if you could make those mutations simply disappear?

That's where the gene-editing tool CRISPR comes in.

CRISPR is made from specialized proteins and other compounds found in certain bacteria.

Normally, these proteins protect the bacteria by destroying enemy invaders like viruses.

But the inventors of CRISPR figured out how to turn those proteins against genetic mutations and other genes linked to disease.

First, they give the proteins coordinates of the wanted gene.

Then, CRISPR runs a seek-and-destroy function.

After that, other molecules are dispatched to repair the gene with new, healthy DNA.

And just like that, you can edit the human genome.

But while the edits may be quick, their changes can last for centuries, especially if you're editing the DNA in an embryo.

Embryos start out with a single cell that eventually replicates into millions and then trillions more.

So if you alter that initial cell first, you're manipulating the ingredients for every cell that follows later in life.

And those same altered cells can be passed on from generation to generation.

That's one reason why most experiments on human embryos haven't left the lab.

That is, except for the work of Dr. He Jiankui.

He claims to have used CRISPR to target and knock out the CCR5 gene in human embryos, which is linked to HIV infection.

And then he did something that shocked the scientific community.

He implanted the embryos into several women, one of whom gave birth to genetically modified twins.

Resistance to HIV aside, most scientists say the procedure was too risky.

At least two studies suggest that edited cells might actually trigger cancer.

And another found that CRISPR can accidentally take aim at healthy DNA.

So while CRISPR could make us immune to disease, who knows what else we might get on the side?