How Does CRISPR Work?

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Fertilized: when referring to an egg cell, combined with male reproductive material to develop a new individual organism.

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

Genome: all of the genetic information of an organism (living thing)... more

Editing Genes from the Start

US Air Force marathon runners

Exercising helps keep us healthy, but what can be done about diseases that are programmed in our genes?

Getting sick can be a pretty awful feeling. We usually try to avoid getting sick by doing things like washing our hands and exercising. Healthy habits may prevent us from getting a cold or a flu, but how would you prevent yourself from getting a genetic disease? You would need to make changes to your genes. And to make sure that you prevent the disease, you would have to have those genetic changes from the very beginning. Germline editing is one way that doctors might be able to prevent diseases before they start.

Germline editing is gene editing of only reproductive cells. These cells are also called germline cells. Germline cells include sperm and egg cells as well as fertilized egg cells, called zygotes.

Germline editing is similar in some ways to somatic editing, but it also differs. Both have the goal to modify the genome to treat genetic diseases. But germline editing is used to try to prevent genetic diseases before they start.

Cell cleavage from one cell to 12 cells

To get a genetic change into all of an individual's cells, the change needs to be made in the egg or sperm. Click for more detail.

By changing reproductive cells, germline editing can affect all of an individual’s other cells. All of an individual’s body cells come from germline cells. So, any genetic edits present in those germline cells will also be present in all of the cells of a fully developed individual. Individuals who develop from edited germline cells will also pass on those edits in their own eggs or sperm. That means genetic changes made with germline editing can be inherited by offspring and future generations.

CRISPR for Future Generations

A developing Xenopus (clawed frog) in an early stage of cell division, with between 4 and 8 cells

If a change is made to an egg or sperm, the change may be present in the fertilized egg. Once in a fertilized egg, the changed DNA is copied into all future cells during development. Click for more detail.

Many genetic diseases are inherited and have no known cure and few treatment options. Those kinds of disease are good targets for germline editing therapies. Germline editing may let us stop some of these genetic diseases before they can affect someone. It would also prevent these diseases from being passed on to future generations.

Germline editing in humans is still heavily debated, but researchers are studying it all over the world. Because it could affect future generations, many scientists and other people worry about its use. There are concerns about the unintended ways germline editing could affect society.

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Bibliographic details:

  • Article: Editing Reproductive Cells
  • 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: June 16, 2021
  • Link:

APA Style

Christian H. Ross. (2019, March 14). Editing Reproductive Cells. ASU - Ask A Biologist. Retrieved June 16, 2021 from

American Psychological Association. For more info, see

Chicago Manual of Style

Christian H. Ross. "Editing Reproductive Cells". ASU - Ask A Biologist. 14 March, 2019.

MLA 2017 Style

Christian H. Ross. "Editing Reproductive Cells". ASU - Ask A Biologist. 14 Mar 2019. ASU - Ask A Biologist, Web. 16 Jun 2021.

Modern Language Association, 7th Ed. For more info, see
embryo development
To edit genetic diseases, genes need to be changed in eggs or sperm, before an individual starts to develop.

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