The Basics: Genetic Editing
Genetic editing sounds like something straight out of science fiction but the truth is that humans have been genetically editing organisms from the moment we first cultivated crops and domesticated animals. Before we could make direct edits to the genome of an organism this genetic engineering would come in the form of selective breeding. No-one at the time would have realised that it was the genetic code that was being altered, all they would have seen was effect on the organism as a whole. This is because our genetic code fuels both variation and uniformity, it underlies some differences seen in people but separates humans from dogs, cats and other animals.
What is genetic editing?
DNA, deoxyribonuclease, contains the genetic code in two intertwining strands, written in the language of four letters. To genetically edit an organism, you modify this DNA code. This modification can take the form of adding or removing letters in the DNA code. The aim is to modify the expression of proteins within the cell, add proteins with novel functions or change the function of pre-existing proteins.
Purpose of genetic editing
There are many reasons to want to modify organisms. You just have to think of all the breeds of dog and all their different roles to understand why there is the desire to change an organism in order to optimise it for a purpose. Genetically modified crops have a bad reputation but the Golden Rice Project was designed to combat malnutrition. There are vast areas of the world where most meals are rice based and vitamin A deficiency is health problem. By modifying rice to contain the precursor to vitamin A, β-carotene, this could easily reduce the harmful side effects of vitamin A deficiency. Medicines are also produced by genetically engineered organisms. One of the first to be licensed for use in humans was insulin derived from genetically engineered Escherichia coli.
Method behind genetic editing
There are several techniques to elicit genetic editing but they all boil down to two steps. Firstly, the section of DNA where the modification is desired is identified and targeted creating a break through both strands of the DNA. In contrast, the second step depends on aim of the genetic editing, whether it is to add or remove bases from the DNA. Both methods rely on cellular machinery repairing the break in the DNA.
In order to add in a new gene, a DNA template of the desired gene is also supplied. The template includes bases that match where the break occurs in the DNA thereby tricking the DNA into thinking a lot of information was lost in the break. As the cellular machinery repairs the broken strand it follows this supplied template DNA including all the new bases.
The other method of repair involves the cellular machinery trimming off the bases either side of the break and gluing the break back together. Through this method of repair some information is lost, therefore it is a good tactic if the aim of the editing is to eliminate the function of the target gene.
Summary
Genetic editing is the process by which the DNA of an organism is modified. This can introduce new proteins, alter already expressed proteins or modify protein expression. There are many reasons to genetically engineer an organism including the production of medicines.
Further Reading
The project to combat vitamin A deficiency through the introduction of β-carotene into a rice strain.
National Human Genome Research Institute – What is Genome Editing?
More detail about genome editing and the incorporation of new genetic materiel into cellular DNA.
History of Insulin – C.C. Quianzon and I. Cheikh
A brief article covering the history of insulin. DOI:10.3402/jchimp.v2i2.18701
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