Blond hair, blue eyes, attached earlobes — certain traits are rare because they require two copies of a gene. That's one of the most basic rules in all of genetics.
But San Diego scientists recently discovered a way to rewrite that rule. They developed a genetic engineering technique so powerful, some experts believe it could be a crucial tool for combating deadly diseases. Others say their experiment was unsafe.
UC San Diego biologist Ethan Bier said it's the coolest thing he's ever seen happen in his lab.
"I was speechless," he said. "It's hard to articulate the degree of surprise."
The jaw-dropping result? Nothing more than a bunch of yellow fruit flies.
Yellow in fruit flies is kind of like blond hair in humans. People need two copies of a gene — one from mom and one from dad — to actually have blond hair. It works the same way in fruit flies.
"You have a yellow gene, which, if you have two mutant copies of it, you have yellow flies," Bier explained. "But if you have only one mutant copy of it, and one normal copy of it, you have the dark pigmentation."
That's why Bier was shocked when his graduate student, Valentino Gantz, came up with a way to ensure every fly born in his lab came out yellow.
Gantz was experimenting with a relatively new genetic engineering tool called CRISPR. He used it to precisely insert the yellow gene into a fly's DNA. He made sure that gene copied itself onto both chromosomes, guaranteeing a yellow fly.
But the modified yellow gene didn't stop there. Gantz got it to copy itself in offspring too, setting off a chain reaction.
"When this gets passed on to the progeny, it happens again," Gantz said. "At each generation it happens in the same exact way.
All the babies from this engineered fly also turned yellow. And so did all their babies, almost without fail. By modifying one single fly, the researchers could turn every fly in their lab yellow within 10 generations, just a few weeks.
"It determines the genetic characteristics of all of their descendants," Bier said. "They are all going to be the same. Which is, like… woah."
If the significance of turning a bunch of fruit flies yellow eludes you, this is how UC Irvine malaria expert Anthony James reacted when he first saw these results:
"I looked at the data and I wrote back. I said, that's what we've been looking for. This looks really, really good," James recalled.
Mosquito-borne malaria kills around 600,000 people every year. But James believes with genetic engineering, it doesn't have to.
James has already discovered ways to make mosquitos incapable of transmitting malaria by altering their genes. The problem is, he can't go around modifying every mosquito in the world by hand.
"What we need then is something that would move these genes into field insects, or wild mosquitos," he said.
If this chain reaction can spread genes through mosquitos as efficiently as it spreads genes through fruit flies, James said it could be a game-changer for countries devastated by malaria.
But the technique won't be used in the field any time soon. For now, scientists say it should remain confined within highly secure labs.
The UC San Diego researchers had to keep their flies in carefully sealed boxes locked behind a series of heavy doors. The facility they used was so secure, it's approved to contain malaria-infected mosquitos.
But let's say one fruit fly had escaped during Gantz's experiment. The worst that could've happened would have been a takeover of yellow flies in San Diego.
But, even that would've been unacceptable, according to Harvard geneticist George Church. He said to think about genetically modified crops. People already distrust GMOs in their food, even after extensive regulation.
"Imagine the reaction of an unscheduled, unapproved release of an aggressively spreading GMO that flies, that doesn't sit still like a plant," Church said.
Church's preferred method of spreading genes includes biological safeguards to prevent modified genes from surviving outside the lab. He said the UC San Diego researchers didn't take that precaution.
Bier agrees safety is a huge concern. His paper called for discussion on developing new safety protocols.
"I do believe that the positive applications of this technology are numerous, and will have real impact on human welfare. And I think that those benefits greatly outweigh the risks," he said.
The domino effect this technique could create would be profound, Bier said. Scientists just have to set up the dominos carefully before tipping one over.
