How Does CRISPR Work?

show/hide words to know

Gene: a region of DNA that instructs the cell on how to build protein(s). As a human, you usually get a set of instructions from your mom and another set from your dad... more

Gene editing: a process where the genome of an organism is changed by adding, removing, or replacing sequences of DNA. This is also called genome editing....more

Prevention: stopping something from happening before it starts.

Protein: a type of molecule found in the cells of living things, made up of special building blocks called amino acids.

Species: typically a group of organisms that are so similar that they can interbreed (have offspring)... more

Template: a pattern or version of an object used as a guide when making a copy or a new object.

You decide that you want to plan a party for you and all of your friends. You have the food, the games, and decorations all planned out. All that’s left is to invite everyone to come over. But how are you going to tell all of your friends?

An illustration of a network of people

If you send your message to a few people, and they each send it to at least one person, and those people do the same, lots of your friends would hear the news. Image by Gerd Altmann from Pixabay.

You could send an individual message about the party to each one of your friends. That would work. But because you have so many friends, it might take a very long time for everyone to find out. It would be quicker to send out a message to just a few of your friends. Then, they could tell your other friends about the party.

So, you decide to send a special message to just a few friends. This message has the party information and one more instruction: to send the message to another one of your friends. Even though you only invited a few friends at first, soon all of your friends will know about your party. This is a lot like how gene drives work.

A gene drive is a tool that forces certain genes to be in a species’ population. Gene drives do this by greatly increasing the chance a certain gene is passed on to an organism’s offspring. So, like with the party invitations, gene drives spread a gene through a species’ population.

Gene Driving School: How Do Gene Drives Work?

Gene drives work by using directed repair gene editing. This enables the insertion of a new gene, called the driven gene, at a particular cut site through the use of a donor template.

Every protein has associated genes that tell cells how to build them, including CRISPR proteins. In a gene drive, both the gene to be spread and genes coding for CRISPR proteins are included in the donor template. The result is that genes for both the driven trait and the CRISPR molecules are inserted at the cut site.

Gene drive inheritance explained visually in a fly population

How does inheritance differ with gene drives? Click for more detail.

Because a gene drive includes instructions to build more CRISPR proteins, it is constantly editing the genome. It even edits the genes that are passed onto future generations to include the driven gene. As a result, the driven gene will soon be present in an entire population of a species in just a few generations.

 

Why Would Scientists Want to Use Gene Drives?

One possible use for gene drives is in the prevention of diseases. Diseases like malaria are carried and spread by mosquitoes. Some people hope to use gene drives to reduce the number of mosquitoes that can carry the disease. Fewer mosquitoes would likely reduce the spread of malaria.

Anopheles mosquito drinking blood from a human

This Anopheles mosquito is one species known to carry malaria. But does this mean that humans have the right to eliminate an entire species? Image by the CDC.

One kind of gene drive that some scientists have suggested is to drive genes that cause only male mosquitoes to be born. Now, you’re right in thinking that this wouldn’t spread beyond that generation. If it worked, there would soon be no female mosquitoes for the males to reproduce with. But, that way, the mosquito population would be greatly reduced. Other types of gene drives have also been proposed. They aim to drive genes that would kill mosquitoes during development to reduce populations.

Despite the benefits, some people worry about how these changes would affects the environment. Fewer mosquitoes may prevent the spread of disease. But it may also negatively affect local ecosystems and food webs. Other people raise ethical questions about if people should even try to eliminate a species at all.

Driving Off Invaders

Another possible use of gene drives is to address the challenges of invasive species. Invasive species are species that are not native to an environment (didn't exist there when we first checked). Invasive species can pose serious threats to the native plants and animals that live there. In those cases, gene drives could be used in invasive species to reduce their numbers in a specific population to almost zero. The goal would be to better preserve native species.

Picture of a bullfrog, a species that is native to the US east, but has moved into areas in the US west.

Bullfrogs are from the eastern United States, but they have been introduced into the western United States. Click for more detail.

But there are several issues with this idea. First, what makes one species belong somewhere more than another? And who are we to decide what species should get to live in one area or another? Using gene drives in this way also raises concerns about long-term effects on the environment. Some people also worry about the ethics of using gene drives to intentionally drive a population to near extinction.

Currently, no gene drives have yet been used in these ways. But there are many scientists that are actively researching gene drives.


Lab mouse image by Rama via Wikimedia Commons.

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Bibliographic details:

  • Article: Gene Drives
  • Author(s): Christian H. Ross
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: March 14, 2019
  • Date accessed: November 18, 2019
  • Link: https://askabiologist.asu.edu/gene-drives

APA Style

Christian H. Ross. (2019, March 14). Gene Drives. ASU - Ask A Biologist. Retrieved November 18, 2019 from https://askabiologist.asu.edu/gene-drives

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Christian H. Ross. "Gene Drives". ASU - Ask A Biologist. 14 March, 2019. https://askabiologist.asu.edu/gene-drives

MLA 2017 Style

Christian H. Ross. "Gene Drives". ASU - Ask A Biologist. 14 Mar 2019. ASU - Ask A Biologist, Web. 18 Nov 2019. https://askabiologist.asu.edu/gene-drives

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/
Lab mouse
Gene drives have been tested in mice, to show that the concept works in mammals.

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