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Genetic modification FAQs

Some frequently asked questions on the topic of genetic modification.

Why do scientists change DNA?

Genome engineering technologies are powerful tools used by researchers around the world. These are used to alter the letters in the genetic code, or DNA, of organisms, to bring about a change in their characteristics.

The oldest form of genome engineering is selective breeding, which has been used since the dawn of agriculture to create the crops and livestock that provide us with food today.

Selective breeding was in use for thousands of years before the genetic mechanisms of inheritance were understood. Today we can use this knowledge, and tools that allow us to analyse DNA, to make the process faster and more precise. The techniques of genetic modification and gene editing allow DNA in an organism to be altered to produce traits of interest in the animal or plant that results.

At the Roslin Institute, we are using these genetic tools to improve animal welfare, promote global food security, and reduce the impact of animal disease on farmed animals and humans.

What are genetic modification (GM) and gene editing (GE)?

Genetic modification is the process of changing the DNA of an organism, such as a bacterium, plant or animal, by introducing elements of DNA from a different organism.

Gene editing involves changing an organism’s DNA by making alterations to its genetic code. These are often small alterations that could happen in nature.

Neither of these is the same as cloning. Cloning creates an exact copy of all or part of an organism’s DNA, while genetic modification and gene editing make changes to existing DNA to create a new, modified version of the genome.

Why do scientists want to make GM or GE animals?

There are many reasons why a scientist would want to alter the genes of an animal for research. Altering the sequence of individual genes can tell us a lot about how that gene works, how it is controlled and how it interacts with biological processes in the animal. Many genetically modified or gene-edited animals are used as models of human and animal disease to help scientists discover new treatments and therapies.

Some researchers at the Roslin Institute study genetically modified or gene-edited animals for one or both of these reasons, and others are interested in studying how to increase the productivity and improve the welfare of livestock animals, such as pigs and chickens. Using these technologies allows our scientists to introduce beneficial characteristics into a livestock breed much more quickly than is possible by normal selective breeding. They can also introduce traits that could not be produced by selective breeding alone. For an example of this, see below.

Does genetic modification or gene editing harm animals?

Some changes to an animal’s DNA can be potentially harmful to the animal, such as changes that cause the animal to develop a disease, which might be carried out so that scientists can learn more about the condition. These changes are made only when there is a very strong case that the research will benefit human or animal health, and scientists always monitor for adverse effects. The Roslin Institute takes the welfare of its animals very seriously and all of our animal research is carried out under strict Home Office regulations.

How do you make an animal using genetic technologies?

There are several different methods that scientists can use to create a genetically engineered animal.

Genetically modified animals have additional DNA elements from a different organism, and gene-edited animals have alterations in their own DNA. Different technologies are used to achieve these two outcomes, but both processes share the same challenge of ensuring that all of the DNA in the resulting animal contains the desired changes.

One approach is to directly inject the modifying technology, such as a genome editor, into one-cell embryos produced by in vitro fertilisation. Because all of the cells in the resulting animal are descended from this single cell, they will all contain the modifications in their DNA. The modified embryos are implanted into a surrogate animal to complete their development, and the resulting offspring is a genetically engineered animal.

An alternative method is to genetically modify the DNA of a single adult cell and develop a cloned animal using somatic cell nuclear transfer (SCNT). This was the method used to produce Dolly the Sheep, although she was not genetically modified as she was created using an unmodified cell.

Stem cells – early stage cells that can develop into various types of specialist cells or tissue – can also be genetically modified and used to make a genetically modified mammal.

A slightly different approach is needed to produce genetically modified birds, such as chickens. This is performed using primordial germ cells – early-stage egg and sperm cells – which can be genetically modified in the lab before being injected into a chick embryo. The modified cells will form modified sperm or egg cells in the resulting hatched chicken. Breeding two chickens that each have these modified cells produces a fully genetically modified chicken.

What are genome editors?

Genome editors act like a pair of scissors, cutting DNA at a specific position in order to make an alteration. Scientists can use genome editors to modify the DNA either by inserting a new DNA sequence at the cut site using a template, or by allowing the cell to repair the cut on its own, which often introduces small random changes at the cutting site. These changes can be as small as adding or removing a single letter of the animal’s genetic code.

Genome editors are easy to use, highly efficient and can be made to target any DNA sequence, which means that they have become very popular. Although there are several different types of genome editor, the CRISPR/Cas9 system is the most commonly used. 

What types of GM animals have been produced at the Roslin Institute?

Many types of GM animals have been produced at the Roslin Institute – examples of some of our projects are below:

Flu-resistant chickens – In the first half of 2015, avian influenza, or bird flu, was responsible for almost US$390 million of losses in the US alone. Research at the Roslin Institute and University of Cambridge has developed chickens which do not transmit bird flu. The chickens were genetically modified to produce a small RNA molecule which mimics the structure of the flu virus and binds to proteins which are involved in viral reproduction.

When these chickens are infected with bird flu, virus replication is blocked. Although the modified chickens themselves can still become infected and succumb to flu, they do not pass the virus on to other birds. We are continuing the project to try to develop chickens which not only prevent transmission of the virus, but are also resistant to flu themselves.

More productive sheep – Genome editing technology is being used at the Roslin Institute to increase the productivity of sheep bred for meat. Naturally occurring mutations that stop a gene called myostatin from functioning have shown that animals with these mutations have up to 20 per cent more muscle mass compared with animals without the mutations. Animals with myostatin mutations convert their food into muscle more efficiently, reducing the amount of resources needed to produce meat. The meat from these animals is also high quality and is low in fat.

These mutations have already been bred into livestock breeds, such as Belgian Blue cattle, but it can take up to 50 years of selective breeding to produce new breeds with myostatin mutations. Research at the Roslin Institute is using genome editors to accurately and efficiently introduce these mutations into sheep to increase their muscle mass. As part of this work, the first genome edited sheep was created in 2013.

Disease-resistant pigs – Porcine Reproductive and Respiratory Syndrome (PRRS) is a viral disease that causes breathing and reproductive disease in pigs. The main victims are new-born piglets who often don’t survive. Infections with the virus cost the pig industry more than £1.75 billion per year in the US and Europe alone. The disease occurs in most pig-producing countries globally, including the UK. Roslin scientists have used the gene-editing tool CRISPR/Cas9 to produce pigs that are resistant to PRRS, by changing the pig’s DNA to remove part of the protein that the virus uses to bind to pig cells. Tests with the virus found the pigs do not become infected. The animals show no signs that the change in their DNA has had any other impact on their health or wellbeing.

Could we eat food produced from GM animals? Would it be safe?

There is no reason to think that the process of genetic modification in food products would be unsafe. However, any new GM plant or animal food product would have to be rigorously tested to ensure that the inserted or modified DNA sequences don’t inadvertently produce any harmful substances, such as toxins or allergens.

Any attempt to introduce genetically modified or gene-edited livestock into the food chain would have to be approved by the appropriate authorities such as the Food and Drug Administration (FDA) in the US or the European Food Safety Authority in Europe.

The first GM animal approved for consumption was the AquAdvantage salmon, authorised by the FDA in 2015.

Related links

Cloning FAQs

GM chickens that don't transmit bird flu developed

Gene-edited chicken cells resist bird flu virus

Gene-edited pigs show signs of resistance to major viral disease

Pig's genetic code altered in bid to tackle deadly virus

Learn more about the CRISPR/Cas9 system []