7.9 Gene editing (New)

In plant and animal breeding the first steps have been taken with gene editing. In this technique the smallest mutation possible at a chromosome can be made precisely at the stage of the single cell: a single nucleotide is replaced by another. This results in another allele with more desirable attributes. A useful application might be the decrease of the frequency of monogenic defects in species of livestock and companion animals, or to avoid the negative effects of the introgression of a desired existing allele from a low productive breed.

Polledness in cattle, the absence of horns, is due to a dominant allele. In some current cattle production systems hornless cattle are desired, but dehorning is an invasive process. Many breeds with desirable qualities have no polled animals or only a few, perhaps with a low genetic merit. Polled calves of horned parents have been born in the USA by using gene editing. But the introduction of polledness can also be carried out without gene editing. It has been achieved over multiple generations by selecting carriers and crossing them with high genetic merit animals of the target breed to minimize the genome contributed by the donors of the polled allele; examples of this process are found in Simmental cattle and in Holstein Friesians. However, the more traditional technique takes about twenty years before sufficient high genetic merit polled animals are available and may introduce a bottleneck into that part of the genome located close to the polling gene, and a loss of selection intensity for other objectives. By repeating the gene editing on multiple individuals within the target breed the time taken to achieve the desired change is much shorter, and the bottleneck can be avoided without reducing intensity for other objectives.

Such applications are very different from gene modification proposed at the end of the 20^th century. Most of the trials intended to incorporate exogenous DNA from other species into another species. They lacked precision in the way the genome was modified, leaving open the possibility of damaging other genes. The trials mobilized a lot of societal resistance against application in a number of countries, e.g. across the EU where these techniques were forbidden. However, the gene editing applications described above do not suffer from these ethical issues that were inherent in this early technology. However, allowing application of gene editing is in the EU still open for discussion in science and in society.