Learn about genes
I’m sure you have heard people say “it’s in your genes” as this is often how we explain the many different characteristics which make each and everyone one of us unique.
In fact, we all inherit two copies of every gene, one from our mother and one from our father. This means that members of the same family tend to be similar, as they are likely to have fewer differences in their genes.
How do genes work?
Our bodies are made up of many tiny units called cells each containing a complete copy of a person’s genes. We all have many thousands of genes and they contain the “genetic instructions” that we inherit from our parents. These “instructions” make us have blonde or dark hair, blue or brown eyes and even determine our body shape. They also control the way every cell in our body develops and grows and what it will do in our body, so they are very important!
Genes are made from a “chemical” called “DNA” (deoxyribonucleic acid) and are arranged in a specific sequence along very long thread-like structures of DNA called chromosomes, rather like a string of beads.
We all have approximately 30 to 40,000 genes stretched out along our DNA. Scientists have discovered what some of these genes do and how changes in these genes can cause particular disorders or diseases. There are however many genes which we still don’t know much about.
The genetic information in the DNA of our genes is in the form of a code and this is known as the “genetic code”.
How does the genetic code work?
It is all rather complicated. You need to think of the DNA being made of 2 strands of a mix of 4 different chemicals called “bases” which face each other and connect as pairs rather like the rungs of a ladder.
We use the first letter of each chemical as our code, so there is: Adenine, Thiamine, Cytosine and Guanine (ATCG). These 4 letters we will call “the DNA alphabet” and in the same way that letters of the alphabet combine to form words and sentences that mean something when we read them, the order of these chemicals are the “letters” which spell out the genetic code and the instructions to our bodies.
A single gene may be many thousands of letters long rather like the MC4R gene shown here.
What do these letters mean?
This is where it gets even more complicated. To be able to understand the code it needs to be read as “3 letter words” called “codons” and each set of 3 letters correspond to another chemical called an “amino acid”.
There are 20 different amino acids that can be made from the different word combinations and our bodies use them to make proteins, often referred to as the “building blocks” of our body. Many different proteins can be made such as keratin in our hair or haemoglobin in our blood to carry the oxygen that we breathe-in to all parts of our body.
So, genes are pieces of DNA that give instructions using chemically coded “messages” that can make proteins for our bodies to use. There may be hundreds, or even thousands, of three letter words in each gene message and sometimes things can go wrong.
What happens when there are changes in the genetic code?
If a single letter (base) in the sequence is out of place, a “spelling mistake” can occur. This can result in different “messages” that our bodies can’t understand, or a protein that doesn’t work properly or at all.
Individual letters or one or more whole words can be missing or even extra to what is required. In fact, even a whole gene can be missing!
As DNA passes from one generation to another through our genes, changes can happen to the code and these changes are known as “mutations”.
What is a mutation?
A mutation or faulty gene is a permanent change in a gene which may cause a problem with the development and functioning of many different parts of our body. Not all mutations cause problems.
A mutation can occur in several ways. Some faulty genes are inherited from our parents and may run in the family. Others can occur spontaneously and are called “de novo” mutations and may explain why a child can have a particular condition or disease even if there is no history of anyone else having the disease in the family.
The DNA code can also be changed by errors in the chromosomes.
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