Genes define who we are, at least in a physical sense, since they determine your traits. A tiny difference in DNA can specify whether you are a human of a chimp.
But how does it work? How can genes, fragments of DNA determine traits? How can genes, for example, determine your eye color, height or even what flowers you like? Let’s find out.
What are genes?
To understand how genes work, you must first understand what genes are. You may have noticed that there are many definitions that I think can be divided into two groups: dictionary definition and molecular biology textbook definitions.
Dictionary will say something like the gene is a unit of heredity and that it transfers information from parent to offspring. That is all true. However, in a biology textbook, you are likely to find that a gene is a DNA fragment that codes for a specific end product. This end product, in most cases, is a protein — a building block of your body.
Both definitions are correct and are often merged. Genes get inherited from parent to offspring; they are heredity units and the reason why you have similar traits with your parents. However, besides that, genes are also a piece of coded information to make the body’s building blocks. What blocks? Let’s say, if DNA is a blueprint for making a body, genes are specific pages to build its parts.
What do genes do and how do they work
If you had a blueprint for making a car, you’d have a page that says how to build a tire. Note though that this analogy is not perfect. To make it more precise, you’d likely have to have detailed instructions on how to build the rubber, how to build the metal casing, how to create different layers of the tire materials and so on. This is what genes do.
For example, there is no gene to make skin. However, there is a gene (or a set of genes) to produce elastin, collagen and other parts that come together to make human skin.
Genes, in essence, are a string of nucleotides, small chemical compounds. You might have previously understood that DNA is a string of letters.
Well, it is, though, the letters are convenient abbreviations for nucleotides. There are four different nucleotides in the DNA — we have guanine, adenine, thymine, and cytosine (G, A, T and C accordingly) and their sequence is what makes genes do what they do.
Our body (and the body of every living organism from bacteria to plants) possess machinery that can read this sequence and understand what to build. I shall dive into this process in some other article, later on, since its slightly complicated: DNA, in fact, is not a template to build a body, it’s actually a template of a template, but let’s not go there yet. For now, understand that genes are a coded blueprint that instructs the body to make itself. It’s no incorrect to say so. You can learn what is DNA here.
Genes are involved in everything your body is or does
Not everything in your body, however, is made directly after a blueprint of genes. For example, melanin determines the color of your eyes and skin. Yet, there is no gene for melanin.
What happens instead, melanin is made through a series of chemical reactions (the process is called melanogenesis) and specific proteins are catalysts for these reactions. So, even though melanin is not a protein itself, its creation is 100% dependent on protein presence. If these genes are active (expressed) in your iris, melanin is made and you have brown eyes.
Note that I did not say whether genes for brown eyes are present in your iris. No, if you have brown eyes, genes to make them are present in every single cell of your body. Therefore, an important part is what building blocks should the body produce, in what parts of your body and in what order.
I am of a caucasian race, and my skin tends to get darker during the summer. Yes, it’s melanin again; we’re not letting it go yet. Melanin is excellent in protection from UV sun rays. Exposure to the sun instructs my body to make melanin, for it protects from sun radiation. So I have these genes to make everything needed for melanin production. Typically, they are “turned off,” and my skin is beige. If I go out in the sun, these genes get activated by sunlight, and over time my skin becomes darker. What determined these changes? Genes did.
Melanin is one example, and we have plenty of them in our body — even more direct ones. For example, a gene INS is a template to build pro-insulin, a protein that undergoes several transformations (assisted by other proteins made by other genes) and becomes insulin. INS gene is turned on/off quite frequently, and its primary activating signal is sugar level in your blood. And guess what? The sugar level is detected by receptors in your body — also proteins. Sugar is then converted to glycogen through chemical reaction orchestrated by yet other proteins.
But its a bit more complicated than that
If this already sounds complicated, you should know this is a massive oversimplification. The main takeaway, genes instruct how to make proteins; proteins make up our body and do or assist almost any physiological process inside it.
To make insulin, you not only need the pro-insulin gene, but you also need many other genes. Finding a single gene that codes for a trait is not easy. Traits are usually a product of many, likely hundreds of genes working together in a complex system. The human body (actually, the body of any animal) is an order of magnitude more complicated than a car or a computer. At least for the foreseeable future.
However, it is still not incorrect to say something like “gene for …. ” because it does not necessarily mean one gene. Sometimes it possible to work with a gene that we haven’t even identified yet. For example, the first genetic map was created for fruit flies in 1913, at that time when there was no definitive proof that genes reside in chromosomes.
There’s an interesting thought experiment: could we find a gene for tying shoelaces? What nonsense, right? Well, actually, it’s not impossible to find a set of genes that are required to tie shoelaces. Say, you will first need to find a group of genes that are required to grow fingers. You should also need some genes to wire brains in a specific way that you are able to learn to tie shoelaces. It gets more complicated with every step, so I’m going to stop here.
The thing is, it is not mandatory to know what genes are involved in determining a specific trait to study them.
Genes are not the only thing that determines traits
Regardless of how complex genes are, they do one thing: instruct the body what parts to make and when. Not all genes become specific end products in all cells. A huge impact of what and when to produce happens while we grow up. That is, while our body literary builds itself.
Sounds funny, but your body indeed gets instructions on how to build itself from genes. Do we grow tall? Genes instruct to make more of us. Do we have curly hair? Genes make proteins that curl hair. Do we… wait a minute. Is it indeed like that?
Of course, to grow tall, we need specific genes that are associated with being tall. We know it is true, because taller people, on average, have taller offspring. But, to grow tall, the body also has to have raw materials (obtained through food) and energy (obtained though food, again). So, it’s not only genes that determine our height, but also our environment. In this case, how much food we had during our childhood.
Another example is about melanin again. I love it and not because I have brown eyes. While genes determine its production indirectly, you noticed it also requires sunshine to turn these genes on. If there is no sunshine, you can have as many genes as you like, your skin will stay pale. Unless your skin is darker from nature, in which case your body does not need sunlight to produce melanin in the skin. That is the only difference between people of different skin colors.
Sunlight is among several things that can turn genes on. Other things are temperature, color, smell, drugs, or even a word you hear. So, in essence, while, in this article, I tried to explain how genes determine traits, it is still essential to know that “determine” is a clumsy explanation of what is going on.