Does Genome Editing cause unintended consequences?

One of the main arguments sometimes levelled against genome editing is the danger of ‘unintended consequences’ – that going in and deleting or rewriting small areas of a genetic code will spill over into parts of the genome it shouldn’t. But is it any different to what happens already?

Listen to molecular biologist, Dr Sarah Raffan, explain what unintended consequences are and how they arise

From the very first crops and domesticated animals to the food in your fridge and the flowers in your garden, humankind has been picking and choosing from the best of nature’s bounty for millennia. By favouring individuals with certain traits, whether it was flower colour, seed size, or milk output, and mating them together, we created today’s myriad breeds, varieties and strains from just a handful of wild species.

Before the advent of biotechnology, such domesticated plant and animal breeding was a bit of a lottery. What started out as putting two likely looking candidates together and hoping for the best had advanced (in plants at least) by the mid-20^th Century to subjecting seeds to either chemicals or radiation to essentially ‘speed up’ the creation of favourable traits by changing their underlying DNA sequence – by what is commonly called mutation.

Mutations, errors during DNA replication, and various other random changes to the genetic code occur naturally - albeit very slowly. These changes are the fuel that evolution runs on. The tiny percentage that confer a benefit quickly spread through a population, often becoming the norm. The majority are disadvantageous and are very quickly weeded out by nature (in what Darwin called Natural Selection).

Through the use of mutagens, plant breeders essentially sped this process up – creating new variation in a plant’s form in just a few generations instead of a few thousand – with the hope being that some of it would produce something beneficial such as a new colour, better flavour, or enhanced disease resistance.

Of course, using chemicals or radiation in this way makes it impossible to target any specific feature. All you can do is cross your fingers that you get something of value. Much of what arises isn’t better and - analogous to what happens in nature - plants with traits that are unwelcome or harmful are quickly discarded (in what Darwin called Selective Breeding).

Over the course of the last seventy years or so, more than 3000 plant varieties, many of which you will have eaten or planted, were created in just this way - using chemicals or radiation to cause new traits to arise.

Today, our genetic understanding and technological advances allow us to focus very narrowly on the traits we want to change. We can go into a plant cell and edit a specific gene rather than hope that bombarding enough seeds with radiation will eventually give us what we want.

Rather than ask if genome editing leads to unintended genetic consequences, it’s better to ask if it leads to more changes, and the answer to that is no, it leads to less. And that’s not only compared to mutagenesis but traditional plant breeding as well.