Mutation and sources of genetic variationSpec 18.1.6, 18.1.7, 18.1.8, 18.1.9, 18.1.10
In short
Mutation is genetic change, and it is the way in which new alleles are formed. Ionising radiation and some chemicals, such as those in tobacco smoke, increase the rate of mutation. Gene mutation is a random change in the base sequence of DNA. Genetic variation in populations comes from mutation, meiosis, random mating and random fertilisation.
Mutation is genetic change. It is the way in which new alleles are formed. Most mutations have no effect or are harmful, but a few can be useful if the environment changes.
Some things make mutations happen more often. Ionising radiation (such as X-rays and gamma rays) and some chemicals (such as chemicals in tobacco smoke) increase the rate of mutation.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanGene mutation is a random change in the base sequence of DNA. It is random because it cannot be predicted which gene will change, or when. A change in the base sequence can change the amino acids in a protein, so the protein may work differently.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanSources of genetic variation in a population
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanFour processes produce genetic variation in populations:
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean- mutation: forms new alleles
- meiosis: makes genetically different gametes with different combinations of alleles
- random mating: any individual can mate with any other of the opposite sex, so different combinations of alleles come together
- random fertilisation: any male gamete can fuse with any female gamete
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanLearn the four sources as a list: mutation, meiosis, random mating, random fertilisation. Do not give the environment: it affects phenotype but is not a source of genetic variation.
Quick check
Define variation.
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Differences between individuals of the same species.
Give two examples of continuous variation.
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Body length and body mass.
Give an example of discontinuous variation in humans.
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ABO blood groups.
What is mutation?
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Genetic change; it is the way new alleles are formed.
Supplement State four sources of genetic variation in populations.
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Mutation, meiosis, random mating and random fertilisation.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026