Gene editing has been the subject of science fiction stories since scientists discovered its role as a code to the development of all life on Earth. Pop culture has used DNA mutation to explain super-powers and animal mutations for decades -- legendary comic book superhero Spider-man got his spider-like strength and web-slinging abilities from a radioactive spider bite. That tale is, of course, extremely far-fetched; but scientists are learning more and more every day about gene editing and how it could possibly be used in the future. In the last 30 years, scientists have studied a method bacteria use to fight off diseases called CRISPR (Clustered Regularly Interspaced Short Repeats) and have been researching ways that it might help humans fight off life-threatening and incurable diseases.
What is genome editing?
DNA is a code written into the foundation of all living things on Earth. It is the process through which all living beings grow and develop. Gene editing is the process by which genetic material can be added, removed or altered anywhere in the code.
Genetic alteration is not a new subject -- humans have been altering the genome of other life on Earth for centuries. From "purebred" dogs to the common banana, selective breeding can be used to alter DNA and choose specific mutations to speed up or reverse the very slow work done by evolution. While "Genetically Modified Organism" has become a scare-word used by industries to sell "Organic, Non-GMO" foods, technically almost all food consumed by humans has been genetically modified through the process of selective breeding. All fruits and vegetables are bred for maximum size and ideal shape, and animals are bred for their fattiness and docile nature.
However, selective breeding can cause significant issues when its used irresponsibly. Purebred dogs, for example, suffer from many horrible diseases and difficulties due to inbreeding and a lack of care on the part of the breeders. Gene editing doesn't rely on primitive, slow techniques with hidden outcomes like selective breeding. Instead, it carefully replaces exactly, and only, the genes specifically identified for particular traits with a different sequence that protects the cell instead of attacking it.
This technique has very obvious uses in humans, such as cosmetic changes to eye color and height, or even practical concerns such as physical vitality. However, scientists are still a long way from being able to edit genetic sequences to produce those traits; currently, gene editing is used mostly for the purpose of research in order to draw closer to a future full of perfect humans.
CRISPRs are a specific kind of gene sequences used in gene editing that creates small spaces in DNA sequences that act as a defense against harmful mutations. If a virus or offending mutation were to appear in the genome, the CRISPR sequence would be able to stop it before it expanded.
How does CRISPR-Cas9 work?
DNA is extremely complicated, and finding and editing many specific sequences in order to create large changes is still a task only evolution has proven capable of. However, inserting changes into a cell is a manageable task. Before CRISPRs, scientists had to use expensive and difficult to produce proteins called ZFNs and TALENs. These proteins needed to be created fresh for every project, and their creation was laborious and sometimes failed. If the experiment were to be unsuccessful, it would mean the loss of thousands of dollars and a significant amount of time. However, CRISPRs are fairly easily and cheaply created in a lab, making them an ideal substitute for previous methods.
Scientists create an RNA sequence that guides Cas9, an enzyme, into a cell's nucleus to remove or edit very specific portions of DNA that would be present due to viruses or diseases. The cell's membrane is breached, usually with a small jolt of electricity, and the RNA is inserted. The RNA sequence guides the Cas9 enzyme directly to the offending DNA strand and the enzyme cuts away the DNA so that it doesn't have a chance to replicate. The cell will then automatically repair itself -- leaving the synthetic structure in the place of the now deleted DNA. The new sequence acts as a defense against the same offending DNA trying to reinsert itself; if the new sequence notices it, Cas9 will automatically be directed to cut it out.
In this way, gene editing isn't done just in response to deadly diseases, but to effectively remove vulnerability from the genome entirely. Because the new sequences do not have any representation outside of the cellular structure, they simply act to make the cell "smarter," and better at defending itself against threats.
Practical applications of the process
So far, the most practical application of the CRISPR sequences has been to study genetics. With this method, scientists can easily see how small changes to DNA will affect single-celled organisms or bacteria. This research is being done with the hope that it will one day soon be capable of doing extremely important genome therapy that could save lives. Prospective parents can have their DNA tested to see if they are carriers for diseases that gene therapy might be able to cure. If there is a high likelihood that a baby would develop those diseases, CRISPRs can be used during in-vitro fertilization to prevent the disease from ever becoming a part of the developing baby's DNA sequence. Not only does this prevent the child from developing those diseases, but it could also prevent them from being carriers, essentially making the gene pool more resistant.
More fantastic ideas about how gene editing can be used are still a long way away. This method is very good at deleting single lines of code that are caused by viruses and mutations that are easy to detect. However, the factors that go into things like intelligence and physical strength are far beyond single line editing in scope. Those kinds of changes may be the future of gene therapy, but until we have a perfect understanding of the many interactions different sequences of DNA have with each other, making those changes can be as difficult and dangerous as selective breeding. Until these methods have been perfected, "designer babies" will still be a thing of science fiction.