• Queen Mary University of London
  • Barts Health NHS

Genes made Easy

Chromosomes from normal human cells. Each colour is a different chromosome. Chromosomes come in pairs.

Scientists around the world are unravelling the mysteries of our genes. Exploring our genes reveals our past and our future, from the diseases you’re more likely to get, to where your ancestors came from. But what is a gene? Where do they come from? And how do your genes make you become you?

Easy explanations of genes and science

What are Cells?

Ostrich egg

Before we can understand genes, we need to talk about cells ! Cells are the basic building blocks of all living things. Human cells are too tiny to see with the naked eye, but your body is made of 1,000,000,000,000s of them. Your cells work together to make your body work. You have hundreds of different kinds of cells in the body, each specially adapted to do different jobs. For example, red blood cells carry the oxygen you breathe around your body.

FUN FACT: The biggest cell in the world is the Ostrich egg, it can be seen with your naked eye.

What is a Gene?

A strand of DNA

Your genes are an instruction manual for your body. Hidden inside almost every cell in your body is a chemical called DNA. A gene is a short section of DNA.

Your genes contain instructions that tell your cells to make molecules called proteins. Proteins perform various functions in your body to keep you healthy. Each gene carries instructions that determine your features, such as eye colour, hair colour and height. There are different versions of genes for each feature. For example one version (a variant) of a gene for eye colour contains instructions for blue eyes, another type contains instructions for brown eyes.


A double helix

What are Genes made of? Hidden inside almost every cell in your body is a chemical called DNA. A gene is a short section of DNA. DNA is made up of millions of small chemicals called bases. The chemicals come in four types A, C, T and G. A gene is a section of DNA made up of a sequence of As, Cs, Ts and Gs. Your genes are so tiny you have around 20,000 of them inside every cell in your body! Human genes vary in size from a few hundred bases to over a million bases.

Every human has around 20,000 genes and 3,000,000,000 bases. Your entire sequence of genes and bases is called your genome.

FUN FACT: your genome sequence fits just right onto a DVD.





 What are Chromosomes? A chromosome is a tightly wound coil of DNA. Chromosomes are found inside your cells. Such tight packing allows the DNA to fit inside a tiny cell. You have 23 pairs of chromosomes in each cell, different types, so that's 46 per cell - a magic number!








finger nails

What do your genes do? Your genes are inside almost every cell in your body. Each gene contains instructions that tell your cells to make proteins. Proteins perform all sorts of different tasks in your cells such as making eye pigments, powering muscles, and attacking invading bacteria. For example some cells use genes that contain instructions to make a protein called keratin. Keratin proteins link together in your body to make things like your hair and fingernails.

Play Genes and Your Cells to explore how different cells use different genes to make your body work.


So: Genes are made of DNA, genes make proteins, proteins make cells and cells make you...

Watch the YourGenome from DNA to protein video to see how it all works


Where do your genes come from? Have you ever wondered why you have the same eye color as your dad or the same hair color as your mum? It’s because you inherit your genes from your parents. You get half from your mum and half from your dad. When you inherit genes from your parents you get two versions of each gene, one from your mum and one from your dad. For example you’ll get two versions of the genes that contain instructions for eye colour. Some versions of genes are more dominant than others; if you get blue-eye genes from mum and brown-eye genes from dad you will have brown eyes because brown-eye genes are dominant. So if you inherit all your genes from your parents, why aren’t you exactly like your siblings?


 Why are you different from your brothers and sister? The reason you and your siblings aren’t identical is because your mum and dad have two versions of each gene, one from each of their parents. When they pass their genes on to you they only pass on one of these versions, and it is completely random which one it will be. For example if your mum has brown-eye and blue-eye genes she could pass the blue ones on to you and the brown ones on to your sibling.

How do genes affect your health?  Your genes are the instruction manual that makes your body work. Sometimes, one or a few bases of the DNA in a gene can vary between people. This is called a variant. A variant means the gene has slightly different instructions to the usual version. Occasionally, this may causes the gene to give cells different instructions for making a protein, so the protein works differently. Luckily most gene variants have no effect on health. But a few variants do affects proteins that do really important things in your body, and then you can become ill.

Play our Gene Finder game to see if you can spot the variant genes.

FUN FACT: blood group O, which is useful because it can be transfused into anyone in an emergency, is caused by a variant in the gene ABO that stops it working (a knockout).


Genetic conditions: Genetic conditions are diseases you develop when you inherit a variant in a gene from your parents. As a result genetic conditions usually run in families. Scientists have identified over 10,000 genetic conditions. One genetic condition is called sickle cell anemia. People with this illness have a variant in the genes that contain instructions to make haemolglobin proteins. Hemoglobin helps your red blood cells carry oxygen around your body. These sickle cell haemoglobin genes cause red blood cells to be the wrong shape, making it hard for them to carry oxygen around the body. Not all gene variants cause a genetic condition. Many variants seem to have no effects at all, others may increase your risk of developing a disease.

Genes and common conditions Scientists are looking for gene variants that can increase your risk of developing illnesses like diabetes, Alzheimer’s and cancer. It’s a tough job as a lot of illnesses can develop in a very complicated way with lots of different genes involved, and they are also affected by environmental factors like how much you exercise, your weight or if you smoke. Rarely, there are women who are particularly at risk of developing breast cancer, because they carry some gene variants. Some of these genes have been identified, and it is now possible to look at people’s genes to see if they are at risk of developing breast cancer. This can save lives.


How does your environment affect you? Your characteristics are affected by your environment as well as your genes. For example you may inherit genes from your parents that should make you tall, but if you have a poor diet growing up your growth could be stunted. To try and understand how much effect your environment can have on you, scientists study identical twins. Identical twins have the same genes, so any differences in personality, health and ability are caused by differences in their environment.

Play Troublesome Twin to discover just how much how much your environment can affect you.

Why do scientists study genes? Scientists have made huge breakthroughs in genetic research over the last few years, learning more and more about our genes and how they make our bodies work. Scientists examine our genes to work out family relationships, trace our ancestors, and find genes involved in illnesses. This gives them the tools to come up with better ways to keep us healthy. A big breakthrough in genetic research came in 2003, with the results of the Human Genome Project.

Watch the Zoom in on Your Genome video


What was the Human Genome Project? The Human Genome Project was an international research study to try and understand our entire genetic code – the complete instruction manual for how our bodies work. Thousands of scientists all over the world worked for over ten years to read every instruction inside every gene of a group of volunteers and put together a picture of the average human genome. They discovered we have around 20,000 genes in almost every cell in our bodies. Most genes are the same in all people, but a small number of genes, less than 1%, are slightly different between people. These small differences contribute to our unique features. Our new understanding of the human genome is leading to many advances in how we treat illness and disease.

How about Personalised Medicine? Soon everyone could have their genes read. In 2015, this costs about £5,000 so is not available to everyone. A doctor might use the information to give you specific medicines, tailored for your genes. At the moment many medicines are ‘one size fits all’, but they don’t work the same way for everyone. Some people respond really well to a medicine, some may not respond at all, and others experience bad side effects. Scientists are learning how differences in your genes affect your reaction to medicines. These genetic differences will help doctors predict which medicines will work for you, so they can prescribe personalised treatments.

Genes can tell us a lot about how to treat and prevent illness, but that's not all... Studying the genes of people around the world can also tell us about our ancestors.


What about the genetics of big populations? Studying your genes can reveal where your ancestors came from. Evidence suggests that humans originally came from Africa and spread out across the rest of the world. As humans migrated around the world, tiny variations in their genes developed. Over time, this happens naturally to help humans survive change. These variants were then passed down through generations. Scientists look at the genes of different populations of people around the world to spot these variations, trace them back though time, and map how our ancestors moved around.


 Genetics is exciting, here's where to find out more


Written by Elise Mullis, David van Heel, Fran Balkwill and Kam Islam.