For decades, scientists encountered seemingly strange sequences within bacterial DNA: small, repeating fragments separated by distinct genetic segments. Initially, their purpose was unclear, yet there was something intriguing about this arrangement. Some of the sequences found between the repeats were virtually identical to fragments of genetic material from viruses that attack bacteria—as if these organisms were storing pieces of their own enemies within their own DNA.
And that is precisely what was happening. When certain viruses, known as bacteriophages, infect a bacterium, they inject their genetic material into the cell, attempting to hijack its machinery to produce new viral particles. However, some bacteria have evolved an extraordinary defense mechanism: they incorporate small fragments of the invaders' DNA into their own genome. If the same virus attempts to infect them again, they use this stored information to recognize it.
This system was named
CRISPR—an acronym that accurately describes the organization of these repetitive sequences. But the most impressive aspect lies in how this defense functions: the bacterium produces small RNA molecules based on the information stored within the CRISPR array. These molecules act as guides, helping specialized proteins locate corresponding sequences within the invader's genetic material. In some of these systems, a protein called Cas9 functions as a kind of molecular scissor. When the guide RNA finds a matching sequence in the virus's DNA, Cas9 can make a cut in that region, compromising the invader's ability to continue its infection. The bacterium had developed a mechanism capable of recognizing and cutting genetic material with impressive precision—and that was when researchers realized something that would completely change the significance of that discovery: if an RNA molecule could guide Cas9 to a specific DNA sequence, perhaps it would be possible to modify that RNA to direct the protein toward other genes—not just viral genes, but genes in plants, animals, and even human beings.
In 2012, Jennifer Doudna, Emmanuelle Charpentier, and their collaborators demonstrated how this mechanism could be adapted to make programmable cuts in DNA sequences—marking the beginning of a transformation in genetic engineering. Until then, modifying a specific gene often required complex tools developed individually for each target; with CRISPR-Cas9, much of that difficulty was resolved by simply altering the RNA sequence that guides the protein.
Instead of building an entirely new tool for every region of the genome, scientists could use a consistent molecular system and simply modify its instructions. DNA had become much more accessible to human intervention—yet cutting the genetic sequence is only one part of the process. Once the DNA is cut, the cell itself attempts to repair the damage. Depending on the strategy employed by the researchers, this repair can either deactivate a gene or allow for specific alterations to its sequence. This is precisely where some of the greatest possibilities—as well as some of the most significant challenges—of genetic editing arise, because DNA does not function like a standard text where one can simply delete a word and replace it with another.
Genes interact with one another, participate in complex processes, and can influence various characteristics of an organism. Furthermore, the editing system must reach the correct cells, recognize the intended target, and avoid unintended modifications elsewhere in the genome. While modifying the code of life has become much easier, predicting every consequence of such modifications has not. Nevertheless, this advancement was so significant that, in 2020, Jennifer Doudna and Emmanuelle Charpentier were awarded the Nobel Prize in Chemistry for their development of a genome-editing method. Just a few years later, this technology evolved beyond a mere laboratory tool: in 2023, regulatory authorities in the United Kingdom and the United States approved one of the first CRISPR-based therapies—a treatment for sickle cell disease, an inherited condition that affects the function of red blood cells.
In this procedure, blood-producing stem cells are extracted from the patient and modified in a laboratory. The goal is to reactivate the production of fetal hemoglobin, which helps reduce complications caused by the disease. The modified cells are then returned to the patient’s body. This is not about rewriting a person’s entire DNA; rather, it is a targeted intervention performed on specific cells for a defined therapeutic purpose. Yet, it represents something that, for a long time, seemed to belong only to the realm of science fiction: a genetic disease being treated by editing the very way human cells function.
And it all began with researchers trying to understand those strange, repetitive sequences found in bacteria.
Nature contains molecular mechanisms that can take us decades to fully comprehend—even after the genes involved have been identified. Now, artificial intelligence is beginning to play a role in this quest. However, there is a significant difference between when scientists first discovered CRISPR and what is happening today: AI is not merely being used to uncover mechanisms that nature has already developed; it is also helping researchers design biological structures that may never have existed before. It is with this shift that we enter a new chapter in history.
