Friedrich Nietzsche said that every man is a unique being and by no chance will “such a marvellously picturesque piece of diversity in unity ever be put together a second time.” The architects of this uniqueness are our genes, so let’s discover how they make each of us one of a kind.
April 25 is International DNA Day when we are celebrating the discovery of the structure of DNA. Back in 1953 a group of scientists, including biologist James Watson and physicist Francis Crick, published papers in the journal Nature on the structure of DNA – the double helix. And then in 2003, it was declared on the same day that the Human Genome Project was completed.
So what better way to honour it than to take a sneak peek inside our cells and learn about the complicated yet fascinating mechanisms of genetics?
Defining a gene
We know that genes are linked to heredity. They are what give us our mom’s curly hair and our dad’s brown eyes. So what is a gene? It is a basic unit of heredity, occupying a specific location on the DNA molecule. Very simply put, genes contain instructions for individual traits of the human body. They do it by directing the synthesis of proteins which in turn affect your eye colour, height, speed of metabolism, and many other traits.
The immortal coil
DNA (deoxyribonucleic acid) is a molecule which contains our genetic information. A DNA molecule is a long chain created from pairs of four chemical bases called nucleotides. Those DNA building blocks come in four varieties: adenine (A), cytosine (C), guanine (G), and thymine (T). They create the following pairs: A–T and C–G. The chain of nucleotide pairs is twisted in a spiral called the double helix. A twisted ladder-like shape, with base pairs in the middle, representing the rungs, and sugar and phosphate molecules forming the ladder's sides. Although nucleotides are the same in every human and even in other animals, it is the order in which they are arranged that creates such an incredible variety of living beings. DNA is in nearly every cell of our body, mostly contained in its nucleus. Human DNA consists of about three billion nucleotide bases.
From DNA to chromosome
Nucleotide pairs, shaped like a double helix, form a DNA molecule, and a gene corresponds to a specific section of the DNA molecule. One gene can consist of a few hundred and up to more than two million DNA bases.
Together with proteins DNA molecule is organized into a threadlike structure called a chromosome. Humans have 46 chromosomes, or, more specifically, 23 pairs of them– one inherited from the mother and the other from the father. That is why we have two copies of each gene – one from each chromosome, one from each parent.
Gene or allele?
Each of the genes comes in two copies, one inherited from our mother and one from our father, and they can give conflicting instructions for a trait that they code for! Let’s look at a simple example – eye colour. We know there are blue, brown, and green eyes with many shades in between, from hazel to grey. So if you have brown eyes and your partner blue, this means that your child will have two different genes for eye colour – brown from you and blue from your partner. This is what we call alleles – different variations of a specific gene. Then how does your body decide which instructions to follow? Some genes are dominant while others are recessive. A gene for brown eyes is dominant to the gene for blue years, which means that your child will have brown eyes. Recessive genes are expressed only if both copies of the gene contain the same instructions – so in our case if both parents have blue eyes.
Your genotype is your complete and unique genetic identity, and your phenotype is a description of your actual physical characteristics from height and hair colour to health and even behaviour.
The driving force behind change and evolution
Genetics and mutation have always played a crucial role in human evolution, from the formation of the first multicellular organism to how we develop modern medicine. The knowledge obtained from looking into our genetic material has already helped humanity a great deal and is expected to play an even more significant part in the future as our understanding of the genetics progresses.
In his incredible work The Selfish Gene, Richard Dawkins said: »We are machines created by our genes.« So hopefully this little excursion in the depths of your cells has given you new knowledge and understanding of the way we function.