Causes of mutationSpec 3.37B
In short
Mutagens are things that increase the incidence, or rate, of mutation. They include ionising radiation, such as gamma rays, X-rays and ultraviolet rays, and some chemical mutagens, such as chemicals in tobacco. Mutations happen naturally at random, and exposure to a mutagen makes one more likely, but it does not mean a mutation will definitely happen.
Mutations happen naturally and at random, but the incidence (how often they happen) can be increased by exposure to certain things called mutagens.
- Ionising radiation, for example gamma rays, X-rays and ultraviolet (UV) rays.
- Some chemical mutagens, for example chemicals in tobacco.
Exposure to a mutagen makes a mutation more likely. It does not mean that a mutation will definitely happen. This is one reason why people are protected from unnecessary exposure to radiation, and why tobacco smoke is harmful.
Exam tip:Learn one radiation example and one chemical example: for instance X-rays and chemicals in tobacco. Say they increase the rate of mutation.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026
Frequently asked questions
What is the difference between mitosis and meiosis?
Mitosis produces two diploid cells that are genetically identical to the parent cell and is used for growth, repair, cloning and asexual reproduction. Meiosis produces four haploid gametes, each with half the number of chromosomes and genetically different from each other. In humans, mitosis gives cells with 46 chromosomes and meiosis gives gametes with 23.
How does meiosis create genetic variation?
Meiosis creates genetic variation because the four gametes it makes are genetically different from each other and from the parent cell. Fertilisation is also random, so any sperm can fuse with any egg. This is why brothers and sisters are not identical to each other or to either parent.
How does natural selection lead to evolution?
Natural selection leads to evolution because individuals in a population show genetic variation and compete for resources. Those with characteristics best suited to the environment are more likely to survive and reproduce, passing on their alleles. Over many generations, the proportion of the population with the advantageous alleles increases, so inherited characteristics change.
All 5 questions on Cell division, variation and evolution
