Conditional gene knockout

The most commonly used technique is the Cre-lox recombination system. The Cre recombinase enzyme specifically recognizes two lox (loci of recombination) sites within DNA and causes recombination between them. During recombination two strands of DNA exchange information. This recombination will cause a deletion or inversion of the genes between the two lox sites, depending on their orientation. An entire gene can be removed to inactivate it. This whole system is inducible so a chemical can be added to knock genes out at a specific time. Two of the most commonly used chemicals are tetracycline, which activates transcription of the Cre recombinase gene and tamoxifen, which activates transport of the Cre recombinase protein to the nucleus. Only a few cell types express Cre recombinase and no mammalian cells express it so there is no risk of accidental activation of lox sites when using conditional gene knockout in mammals. Figuring out how to express Cre-recombinase in an organism tends to be the most difficult part of this technique. ==Uses==

The conditional gene knockout method is often used to model human diseases in other mammals. ==Knockout Mouse Project (KOMP)==

Conditional gene knockouts in mice are often used to study human diseases because many genes produce similar phenotypes in both species. For the past 100 years laboratory mouse genetics have been used for this because mice are mammals that are physiologically similar enough to humans to generate qualitative testing. These two have such similar genes that out of 4000 studied genes, only 10 were found in one species but not the other. All mammals shared the same common ancestor approximately 80 million years ago; technically speaking, all genomes of mammals are comparatively similar. However, in comparison between mice and humans, their protein-coding regions of the genomes are 85% identical and have similarities between 99% of their homologs. These similarities result in similar phenotypes to be expressed between the two species.[8][12] Their genes are very alike to those of humans with 99% having homologs being similar. Along with producing similar phenotypes as well making them very promising candidates for conditional gene knockouts.[8] The goal of KOMP is to create knockout mutations in the embryonic stem cells for each of the 20,000 protein coding genes in mice. The KOMP project contributor, Oliver Smithies, arguably provided the biggest scientific impact on this gene targeting. Oliver received the Nobel prize for medicine due to a technique allowing the ability to identify functions in genes and how to use the 'knockout' method to delete certain genes. Unfortunately, the pioneer in gene targeting died at the age of 91 on January 10, 2017.[11] The KOMP projected was started in 2006 and is still ongoing today. The KOMP Repository provides incentives to those partaking in the projects to return feedback to them and those who meet specific criteria can be refunded 50% of the cost of their research cells.[10] ==References ==