Genetics / genomics · BEGINNER LESSON
Knockout
A knockout is a genetically engineered organism in which one or more specific genes have been made nonfunctional or removed. In genomics, the goal is to stop the gene from working so researchers can observe what changes in the organism.
What a knockout is and what is measured
A knockout is not a natural “missing feature”; it is a laboratory-made change in DNA. Researchers measure the organism’s traits, called phenotypes, after a gene has been inactivated. A phenotype is any observable characteristic, such as growth, tissue changes, or disease-related features. Comparing the altered organism with an unaltered one helps show what the gene normally contributes to development, body function, or disease-related traits.
[1] www.genome.gov › genetics-glossary › KnockoutKnockout - National Human Genome Research Institute [2] Knockout Mice Fact Sheet [3] The Knockout Mouse Project - PMC - NIH
How knockouts are made
One common approach is gene targeting, also called homologous recombination. Homologous means the inserted DNA has matching sequences that line up with the target gene, so the cell’s own repair machinery swaps the old gene segment for inactive artificial DNA. Another method is gene trapping, where artificial DNA inserts randomly into a gene and disrupts RNA splicing. RNA splicing is the step in which a newly made RNA molecule is edited before it can direct protein production. Both methods can be done in cultured cells, then the altered cells can be used to produce mice.
[2] Knockout Mice Fact Sheet [3] The Knockout Mouse Project - PMC - NIH
Why knockout mice are useful
Knockout mice are widely used because mice share many genes with humans. If removing a mouse gene changes the mouse’s traits, that gives clues about what the corresponding gene may do in humans. This approach has been useful in studies of cancer, obesity, heart disease, diabetes, arthritis, substance abuse, anxiety, aging, and Parkinson disease.
[2] Knockout Mice Fact Sheet [3] The Knockout Mouse Project - PMC - NIH
Limitations and caution
Knockouts do not always give a simple answer. About 15 percent of gene knockouts are developmentally lethal, meaning the embryos cannot survive to become adult mice. Also, a knocked-out gene may produce no obvious visible change, or the same gene may matter differently in embryos and adults. A gene’s effect in mice can also differ from its effect in humans, so knockout results are informative but not a direct copy of human biology.
[2] Knockout Mice Fact Sheet [3] The Knockout Mouse Project - PMC - NIH
Related terms
A homozygous knockout means both copies of a gene, one on each chromosome, are inactive in all tissues. A reporter gene is an added DNA marker used to track where the altered DNA is present or active.
[2] Knockout Mice Fact Sheet [3] The Knockout Mouse Project - PMC - NIH
SEE THE IDEA
How a knockout is used to study gene function
A specific gene researchers want to study
Gene targeting or gene trapping disrupts the gene
Cells or mice carry the knocked-out gene
Researchers compare phenotypes to infer gene function
Researchers inactivate a gene, then observe resulting traits to infer what the gene normally does.
A knockout links a DNA change to observable traits, but the results can vary by development stage and species.
TRY IT YOURSELF
Test your understanding
Choose an answer, then check the explanation.
PUT IT TOGETHER
Match each concept to its meaning
Drag a label onto its description, or select a label and then select a description. This also works with a keyboard.
4 pairs to match
Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.