“Interaction between gene and environment or G*E can produce variable phenotypes- either helpful or harmful.”
Genes- the sequences of the DNA that are the long chain of the nucleotides, and are important for us, in fact, for every life on the earth. It is known as the building block of life which makes different proteins for us.
Genes are the coding sequences of the DNA, actually, is the lesser part of our genome but is important as well. As genes express, phenotype produces, phenotypes are the visible characteristics of organisms.
Some changes- means alterations are truly helpful for us. For instance, the change in the skin color; on the other side, some are so harmful like the sickle-cell allele.
But overall alterations in the phenotype are very important for life on earth to survive.
Read more on Genotype vs Phenotype.
Change is everything, change is a must!
‘Evolution’- an important phenomenon on earth is driven through various forces cause change- alteration or polymorphism. Genotype or genetics is one of the forces that have driven the process of evolution.
Simply put, we can say, what we are today is because of the continuous changes in our genes or genome through the process of evolution.
But the question arises how changes occur in the DNA or genes, is there any other forces! The answer is yes, “environment”- one of the many factors that produce various phenotypes.
The environment here is our surroundings- the temperature, heat, atmosphere, pollution, water, humidity or everything around us is an environment for us.
“What we eat has a definite effect on our body, we know that.”
Scientifically it is proven that interaction between genes and environment altered phenotypes and drive the evolution of new traits. Yet it is not understandable for so many others, let us understand it with examples.
Eye coloration and temperature:
The temperature has a significant effect on eye coloration. A bunch of genes from our genome have a role in developing eye color. There are more than 150 various genes that have a definite role in eye coloration, along with it, not only those genes but also the temperature (extrinsic environmental factor) decides eye color.
OCA2 is a candidate gene for deciding eye color and is linked to the melanin synthesis pathway. Higher melanin produces under higher temperatures to protect the skin, eye, or epidermis.
OCA2 and other genes expressed higher in the eyes make it darker in those living at a higher temperature.
Contrary, people living at low temperatures have light eyeshades (generally) and have less melanin in their iris. The reason is again clear, no additional protection is needed.
Read more: Comparison Between Gene vs Allele.
Drought resistance in plants:
Developing drought resistance plant species are economically important. A special set of genes (more than 60 different genes) in the entire plant kingdom gives a drought resistance power to plants.
Under the influence of drought, they express more and help the plant to sustain. Drought is one of the environmental factors.
Sickle-cell allele and malaria parasite:
Sickle allele, an altered form of the HBB gene was originally evolved to give resistance against the malaria parasite. With a single sickle allele, red blood cells become sickle-shaped which are not recognizable for malaria parasites and can’t infect, consequently.
Over a course of evolution, the sickle allele was evolved for a novel cause, unfortunately, two sickle allele causes a severe type of anemia and is not treatable.
The rate of skin cancer is higher in bright skin people, living at a higher temperature. The bright or white skin tone was evolved originally to survive at a lower temperature.
Genes to code for melanin, expressed in a lower amount under low temperature and skin tone becomes more bright. Although, when they try to live in a higher temperature area, the activity of melamine disrupts and causes skin cancer, in most cases.
The extra layer of the melanin protects our skin from harmful UV effects hence those having higher Melaine can resist the harmful UV radiations easily in comparison with others.
These are the classic examples of how genes and environment interact and produce different phenotypes, traits, changes and diseases.
The same interaction is also responsible for the production of congenital disorders as well. The adverse extrinsic environment influences the gene expression profile of a developing fetus and alters genotypes from normal to abnormal and subnormal conditions.
The nature of the disease, the severity of the disease and even the dose of the drug against the disease can be decided by studying the gene environmental interactions. For instance, some people can respond to some specific drugs under the influence of some specific environment while other classes of peoples can’t respond to the same drug.
Examples make it clear that the environment makes interactions with genes, alters gene expression as per the need and produces a different phenotype.
However, it is not the case for all. Sometimes, this interaction which is very essential and important too causes adverse effects as well.
One of the best example for it is the sickle cell trait or sickle allele, we have discussed already.
Adverse effects of gene-environment interaction can cause harmful effects and produce disease. Cancer, congenital abnormalities, metabolic and other problems occur from it.
The gene environmental interaction studies are helpful in pharmacogenomics as well.
Now scientists are trying to study the gene expression of people of different regions to evaluate the fact that different groups of peoples react differently under different environments.
In layman, you can understand it by this simple example; saffron can grow only in some regions of the world, the reason is, only those conditions are favorable for it and genes of saffron plant express stably.
Now here is the point studies of GE interaction helps in manufacturing genetically modified organisms. We can create a GM- saffron plant to grow it in some other adverse environment.
Do it yourself! You can understand the mechanism of gene environmental interaction by conducting a small experiment at home.
Grow two sets of plants one commonly present in your region and another set that is not present in your region. Observe the differences after a few weeks.
Technically, the environment can influence genes in two different ways. One it directly changes the composition of a gene viz change the bases of genes- mutations.
Second, it changes the expression of genes- the amount of genes produces to makes the protein in the different bodily cells, in this case, it can’t change the structure of a gene.
But using either of ways alters the governing phenotype. Which is, as we said, harmful or helpful- only nature will know!
So here is the simple explanation of how gene and environment interact with each other and changes the phenotype of the organism, however, the entire study is a broad subject and is a combination of genetics, population study, statistics, evolutionary study.
I hope this article will help you to understand the present mechanism briefly. Though most of the studies of the gene environmental interaction are under the experimental phase.