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CRISPR, the fancy new technology that lets people edit genes, could have an unprecedented and horrific consequence

Scientists are abuzz over a new technique that lets people edit the genes of practically any animal.

The method, known as CRISPR, holds the potential to fix genetic defects that cause disease in humans. And researchers are also experimenting with tweaking the genes of other animals. For example, you could modify mosquitoes to prevent them from spreading horrific diseases like malaria and dengue fever, or make agricultural crops resistant to pests.But this could go terribly awry if one of these tweaked genes, which research suggests could spread through a population like wildfire, turned out to have unintended effects.In a recent study, team of scientists at Cornell University created a mathematical model for how quickly and extensively one of these modified genes spread through a population, a phenomenon known as gene drive.Their findings were disturbing: It took only a few tens of generations for the tweaked gene to become widespread in a population. By comparison, a naturally occurring gene could take hundreds of generations to reach the same frequency, the researchers said.
Tinkering with nature
Normally when two animals reproduce, the offspring inherits two copies of a gene, one from each parent. But in previous research, scientists at UC San Diego figured out a way to use CRISPR in fruit flies to change one of these copies into the other, desired copy of the gene. The resulting flies got two copies of the desired gene, ensuring it would get passed on to any offspring they had.In this way, the tweaked gene could rapidly spread through an entire population. That gene could be one that makes male mosquitoes sterile, for instance.In nature, genetic mutations that cause changes in a single copy of a gene are almost always lost, because most mutations are bad, so any animal that gets two copies is unlikely to survive and reproduce. But the Cornell researchers found that under the right conditions, introducing a tweaked gene in one individual spread to the entire population almost one-third of the time.This could have some horrific consequences.For example, the gene might get into a population you don't want it in. Say we tweaked a gene in mosquitos carrying dengue fever to protect humans from the disease, but the modified gene somehow jumped into a related species and wiped it out. At worst, the gene could be transferred (by a mite or wasp) to honey bees, whose populations are already suffering from mysterious declines. If the gene ended up wiping out bees, suddenly we'd have a hard time pollinating our crops.The technology is still very new, and we are just beginning to understand its possible consequences.
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