“Our genomes carry the story of evolution, written in DNA, the language of molecular genetics, and the narrative is unmistakable,” said Kenneth R. Miller, American cell biologist, molecular biologist, and former biology professor.
The words are the genes, the sentences are the chromosomes, and the entire story is the genome. The genomes are the creators or the builders of the living world around us. If genomes make us, then would genome editing modify us? Before pondering the answer to this question, let us dive deeper into understanding what genomes are.
Understanding Genomes
“You look exactly like your dad.”
“Your hair is like your mother’s.”
These are the comments we all hear now and then. Of course, we would carry the traits of our parents. It is evident because our DNA is formed with 50% of the father’s and 50% mother’s DNA.
DNA is the genetic material that carries the genetic information; many of our hereditary characteristics are from the DNA. You would be surprised to know that DNA not just carries genetic information but has different functions divided among the parts of DNA. The part of the DNA that carries the instructions for building up the molecules is called genes.
The part of DNA that doesn’t carry any code for building cells was previously called junk DNA. But recent discoveries have found that even junk DNA has functions related to controlling different gene activities.
Genetic information would not only determine visual characteristics such as height and colour. Genetic information also determines hereditary diseases, resistance power to infections, and many more aspects.
The entire genetic material, with all the genes and the junk DNA together, is known as the genome.
The code game of the DNA
The code in the DNA decides what you are, from the species you belong to to the characteristics you possess. But do you know how it does that or carries the information? It does through the codes. The four chemicals, adenine (A), thymine (T), guanine (G), and cytosine ( C), are arranged in a specific format or sequence that forms the code.
The sequence of these chemical compounds, also called nucleotides, carries all the information from the structure of a single cell to the entire organism. For example, the computer knows only zeros and ones; similarly, DNA knows these four chemicals A, T, G and C.
The genome also carries and takes care of genetic information, but also different functions of individual cells in the body are taken care of by the genome.
Decoding the code – Genome sequencing
Studying the code of the genome in individuals is genome sequencing. We decode the order in which the four chemicals or nucleotides are arranged in the genome of the particular species and individual.
The genomes are supposed to be identical in an individual organism, but some impact of environmental factors or some mutations (DNA carries the wrong code or sequence) might vary the genome and would impact the life of the organisms. ng code or sequence) might vary the genome and would affect the life of the organisms.
Cancer, which is the cell’s fast division, might be caused by such mutations. The misspelt code might be a code to instruct faster cell division.
Genome editing
Genome editing is, as the name says, the editing of an individual genome. In a preferred location, the DNA can be added, deleted or replaced based on the requirement.
Simply put, it is editing the wrongly written code; it would mean deleting, adding or replacing the code or the required order of the four chemicals at a required location.
There are different types of Genome editing possible.
Homologous recombination:
Through this method, the code or the sequence of the genome we need to edit would be known. We then create a DNA strand that matches the one that must be edited. This created DNA is injected into cells.
These injected strands would then combine with the DNA fragment already in the cell. And we would have the edited genome.
But this has the drawback of genome recombination or editing occurring at unwanted locations.
Zinc-finger nucleases (ZFN):
It is an improved technique for editing specific locations, unlike homologous recombination.
ZFN, unlike homologous recombination, is an improved technique for editing the genome of specific locations. Here the natural proteins are used to build the DNA sequence. This sequence would bind to their particular location and cut the DNA. Later the editing would be done through homologous recombination.
Though this technique guarantees that the edit will happen in the required place, creating protein sequences is time-consuming.
Transcription activator-like effector nucleases (TALENs):
These are similar to the ZFN but use different proteins, which are easier to engineer than the ZFNs.
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR):
It is a much improved and easier technique to implement. This technique uses Cas9 (bacterial immune protein / RNA-guided enzyme) to cut the genome at a specific location.
It is inspired by bacteria, which uses Cas9 to kill viruses. It is now used in genome editing.
Instead of creating the DNA sequence with proteins, RNA* is created. This RNA would match the DNA that has to be edited, and the RNA is much easier to create than the proteins in previous techniques. Also, the portion of RNA created can guide the Cas9 protein to the exact location that has to be edited. That portion of RNA is called “guide RNA”. Once at the location, the Cas9 cuts the genome, and the RNA proceeds with the recombination.
This technique is six times better and easier than the previous techniques.
Latest genome editing applications and research:
Antimicrobial Resistance(AMR):
The latest threat humanity faces with health is antimicrobial resistance (AMR). The bacteria, viruses and fungi have evolved and don’t respond to the drug/medicine that kills them.
The medicines that would treat your cough or cold due to some bacterial infection; might not work the same few years down the line. The bacteria would have changed its genome, so the medicine has no impact. This change in the genome is through mutation.
The latest genome editing technique, CRISPR, is used to fight the resistance the bacteria has developed against the medicine. The mutated genome, which ensures medication doesn’t have an impact, is cut and deleted.
In a recent research study, the genome of the bacteria responsible for resisting medication was cut out successfully. It was also ensured that this resistance would not develop in the future.
Genome editing in treating inherited diseases:
Active research is going on to use genome editing technology to treat various diseases inherited through genetic material. For example, diseases such as sickle cell, a deformed red blood cell whose deformation is due to an error in the code that impacts the oxygen supply.
Conclusion
Genome editing would significantly impact agriculture’s health through editing genomes. The techniques have been used to improve agricultural yield in adverse weather conditions.
Similarly, one day we might or might not find the solution to global warming but might edit the human genome to live in adverse conditions.
Do Share your opinions on the topics; we await hearing them.
*RNA is similar to DNA but is a single strand rather than a double helix strand, as in DNA. It transfers just the genetic code to build the proteins.
Reference:
- https://www.genome.gov/about-genomics/policy-issues/Genome-Editing/How-genome-editing-works
- https://scitechdaily.com/harnessing-gene-editing-in-the-fight-against-antimicrobial-resistance/
- https://www.genomicsengland.co.uk/genomic-medicine/understanding-genomics
- https://jcottonres.biomedcentral.com/articles/10.1186/s42397-023-00140-3
- https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.001334?TRACK=RSS