Scientists working at the University of California have developed a form of gene drive to control the inheritance of multiple genes in mice. Until now, such technology has been limited to the control of inheritance in insects only.

Gene drives are a type of engineering technology which propagate one particular set of genes through a population by changing the possibility that a specific allele will be given to children. These drives are ethically questionable, with criticisms raised that they can radically and swiftly change an animal population.

In their paper appearing in Nature, the scientists announced that they had engineered an active genetic “CopyCat” DNA element to control a rat’s fur colour. This disrupts both copies of the mouse’s genes which dictate a black colour, ensuring the mouse’s children are white instead.  

The CopyCat element was designed to ensure it could not spread to the rest of the rat population, so that it is carefully controlled by scientists.

The scientists found some difficulties in transferring the gene drive technology to mammals, and particularly to making it work during the production of sperm in male mice, however: “Our comparison of eight different genetic strategies indicates that the precise timing of Cas9 expression may present a greater challenge in rodents than in insects to restrict DSB formation to a window when breaks can be efficiently repaired by the endogenous meiotic recombination machinery. Nevertheless, the copying efficiencies that we observed here would be more than sufficient for a broad range of laboratory applications.

“For example, the average observed copying rate of 44% using the most efficient genetic strategy in females combined ultra-tightly linked tyrosinase mutations such that 22.5% of all offspring inherited a chromosome with both alleles, which would not be possible through Mendelian inheritance.”

They said the difficulties could be due to the timing difference of male and female meiosis. Even with that being the case, the mechanism only worked around 70% of the time in females at best.,

The scientists are now attempting to expand the tool to multiple genes and traits.