Genetic disorders

Aadesh and his younger twin brothers are drawing, and Aadesh can’t find some of the colours. Rohan, could you pass me the green colouring pencil please? This one? No, that one’s yellow. I can’t tell which one is which!

It seems like Rohan and Mohan can’t see colours the same way Aadesh does. They are colour blind. What is the reason for this? If we look at their family tree, we can see that their grandad was colour blind too. Maybe the twins inherited something from him?

Different traits, for example the ability to see colour, are passed down through generations. These traits are controlled by genes. Genes are organised into chromosomes. Humans usually have 46 chromosomes. Two of them are so-called sex chromosomes - the X and the Y.

We get 23 chromosomes from the mother and 23 from the father. Sometimes a gene or genes on a chromosome change, mutate. In the case of Aadesh’s grandad, it was the genes that control the ability to distinguish colours that carried the mutation. These genes are only found on the X chromosome, which Aadesh’s grandad passed onto his daughter, Aadesh’s mum. She wasn’t affected because the genes on the X chromosome she received from her mother weren’t mutated.

But she became a carrier, a person who can pass on the mutation, while not being affected. By chance, Rohan and Mohan received the X chromosome with the mutated genes, while Aadesh didn’t. Colour blindness is a genetic disorder. But sometimes, a mutation in one single gene is enough to cause a genetic disorder. One example of such a disorder is when a mutation causes abnormal red blood cells.

This is called sickle cell anaemia. Sickle cell anaemia is very common in Sub-Saharan Africa. To some extent it can protect from malaria, but it can also cause major health issues. Genetic disorders can also be caused by an abnormal number of chromosomes. One of the most common is Down’s syndrome.

This occurs when a person has 47 instead of 46 chromosomes, specifically one extra copy of chromosome 21. Genetic disorders can seriously affect people’s lives, cause health problems, or lead to premature death. We can’t cure genetic disorders, but some therapies and new technology can often help relieve symptoms. And scientists are persistently researching causes and developing new therapies, some that could even change genes back to normal. Maybe we could buy you some glasses that would help you distinguish colours?