Genome editing is seen by many as a way of speeding up genetic progress, but what could the future hold for the technology.
or centuries farmers have used selective breeding to improve the production, conformation and health traits of their livestock. And with advancements in technology such as artificial insemination and more recently genomics and IVF, the speed of genetic gain has continued to increase.
In cattle traditionally it takes at least three years for benefits of superior genetics to be felt and often visible results are only seen after decades of selective breeding.
However genome editing claims to provide an answer to this problem, it is it could be used to introduce useful genes into a population even faster than traditional breeding.
Prof Mike Coffey, professor of livestock informatics at Scotland’s Rural College (SRUC) says: “Most traits of economic importance in livestock production are polygenic, meaning they are controlled by hundreds or even thousands of genes.
“But in some cases phenotypes, can be changed dramatically by just changing one gene, a good example of this is disease resistance in fish.
“Changing the base proteins from A to T or C to G means the expression of the gene can be altered significantly, producing a difference in the phenotype.”
Research on genome editing to date has mostly looked at making improvements to disease resistance, production and welfare as well as looking for ways to remove allergens from dairy products.
Scientist in Brazil recently began a study to address the welfare issues surrounding mechanical dehorning of cattle and aimed to breed a herd of gene-edited polled cattle.
They used a bull called Buri, which had a polled gene inserted into its genome through gene editing.
However, in the case of Buri, it was discovered, accidentally, that not only had the intended DNA template attached to the DNA sequence, but the whole plasmid. Essentially, the bull was cross-contaminated with bacterial DNA and 4,000 of his base pairs out of about 3 billion in fact belonged to a bacterial organism.
In addition to this, these plasmids often carry genes that are associated with resistance to some antibiotics used to treat common cattle ailments.
Although there was no indication the mutation found was unsafe, there was also no guarantee that it was.
Heather Lombardi, director of animal bioengineering at the US Food and Drug Administration (FDA) says: “Ultimately the finding shows that scientists still have much to learn about gene editing, and that it clearly is not just a quicker form of selective breeding. It is still a young technology and there are improvements that are still being made.”
Gene editing and genetic modification is not permitted in the UK for use in commercial agriculture and it is currently illegal for any animal which has been genetically engineered, or originates from parents which have, to enter the food chain.
Gene editing is carried out by using enzymes which act like molecular scissors and are used to cut the DNA in very specific targeted positions. When the DNA is broken, the cell wants to repair itself, and this repair process can then be manipulated by scientists by inserting new material called DNA templates.
The DNA templates are introduced into the cell using a vector, usually a bacterial molecule called a plasmid. The DNA template then attaches to the newly exposed ends of DNA where the cut took place, changing the sequence and ultimately the expression of the gene.
Prof Coffey says: “There are significant differences between genome editing and genetic modification (GM).
“Gene editing only requires the base protein to be changed, a switch that could easily happen naturally as a mutation, however GM refers to inserting DNA from different species to gain desirable traits.”
“If gene editing is going to be able to be used and be accepted by consumers it is important it does not get put under the GM banner.”
Prof Coffey says people’s perceptions change depending on the circumstances, if grass could be genetically altered so that when cows eat it they would produce less methane people may feel this is more acceptable in the face of impending climate change.
He says, for genome editing to gain a license for general use it will have to satisfy the food standards agency (FSA) that consumers will not be offended by it.
“We will have to prove that it is beneficial, it is probably best to start with looking at disease resistance or environmental benefits which could be gained. I think consumers would be less likely to support gene editing for simply producing better tasting meat or eggs.”