 You've probably watched a movie or read a comic book about a person who got superhero powers because of a mutation. Unfortunately, this is science fiction. In real life, a mutation won't give you superhuman strength or the ability to read people's minds, but they can cause a change, albeit not so exciting ones. The mutation is a change in DNA. It happens where one or more nucleotides is deleted, inserted or substituted for a different nucleotide. This results in a change in the sequence of the nucleotide's basis. If this change occurs in a gene, it can alter the order that amino acids are coded for, which in turn will change the shape of the protein. A change in a protein's shape can result in the protein acting differently or not working at all. For example, if there is a mutation in a gene that codes for an enzyme, the resulting protein chain that is produced might not fold in to the correct shape, so the active site of the enzyme no longer fits the substrate. The majority of our DNA does not code for a protein. This is called non-coding DNA. In fact, only 1% of the 3 million nucleotides that make up human DNA are actually protein coding genes. That's a tiny amount. Some of the non-coding DNA regions do however have other roles, such as controlling if and how genes are expressed. Whilst mutations can occur to a gene itself, they might also occur in an area that controls if a gene is expressed. And therefore, whether a particular protein is made, thus mutations in these non-coding expression sections can also affect phenotype by altering gene expression. More often than not, a mutation occurs in a region of the DNA that does not code for a protein or control expression. This means that most mutations have no effect on phenotype. Look at everyone around you. Maybe they have different hair or eyes or skin colour. There is a lot of genetic variation in all populations, humans, animals, plants, everything. This is because genetic variation in a population arises from mutations. For example, in a population of black mice, a mutation might arise which causes white fur. This mutation would not be an advantage to mice living in the wild, because the white mouse would easily be spotted by predators and eaten. It is not likely to survive to adulthood and breed to pass on this white hair gene to its offspring. However, if a mutation causes a new phenotype that is useful, such as better hearing, then the new gene will get passed on to offspring and the number of mice in the population with this new phenotype will increase. This gradual change in a population is known as natural selection and is the mechanism by which evolution occurs, which you can learn more about in other videos. In populations of bacteria, mutations often occur which, by chance, gives an individual resistance to antibiotics. Because this is an advantage and bacteria reproduces so quickly, this mutation can spread very quickly throughout a population. This is how antibiotic resistant bacteria evolve and is a problem for humans. So what causes mutations? Well, this is where science fiction meets science fact. Sort of. In the backstory of many superheroes, there will be a meeting with a radioactive substance, be it cosmic rays or radioactive waste. In real life, exposure to ionizing radiation, such as gamma rays, x-rays and ultraviolet rays and some chemical mutagens, like chemicals in tobacco, can increase the incidence of mutations. If these mutations happen to a region of DNA that controls cell division, cancer can occur. This is because cancer is uncontrollable cell division, thus exposure to ionizing radiation increases the risk of developing cancer. For example, UV light is a risk factor for skin cancer and smoking is a risk factor for lung cancer. To learn more about cancer, watch this video. In this video you have learned about what a mutation is, how it can affect the phenotype of an organism and what causes mutations.