Variation — Cambridge IGCSE Biology
Continuous and discontinuous variation, what causes them, and how mutation and other processes create genetic variation.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Variation is the differences between individuals of the same species. Continuous variation gives a range of phenotypes between two extremes, such as body length, and is caused by both genes and the environment. Discontinuous variation gives a limited number of phenotypes with no intermediates, such as ABO blood groups, and is usually caused by genes only.
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.
Exam questions
7 exam-style questions (19 marks), each with its mark scheme.
Answer the questionsFlashcards
9 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of variation and selection on one page, so you can see where this subtopic fits.
Open the mind mapPractical sheet
Method, variables, risks and a results table, with questions to answer.
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Free PDFs to print or save.
Quick check questions
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.
Frequently asked questions
What is the difference between continuous and discontinuous variation?
Continuous variation gives a range of phenotypes between two extremes, such as body length or body mass, and is caused by both genes and the environment. Discontinuous variation gives a limited number of phenotypes with no intermediates, such as ABO blood groups or seed shape in peas, and is usually caused by genes only.
What causes genetic variation?
Supplement Genetic variation in a population is caused by four processes. Mutation forms new alleles. Meiosis makes genetically different gametes. Random mating brings different combinations of alleles together, and random fertilisation means any male gamete can fuse with any female gamete. The environment affects phenotype but is not a source of genetic variation.
What increases the rate of mutation?
The rate of mutation is increased by ionising radiation, such as X-rays and gamma rays, and by some chemicals, such as the chemicals in tobacco smoke. Mutation is genetic change and is the way new alleles are formed. Most mutations have no effect or are harmful, but a few can be useful if the environment changes.
Which graph do you use for continuous variation?
Continuous variation is shown on a histogram, with the bars touching, and the shape is often bell-shaped. Discontinuous variation is shown on a bar chart, with the bars separate. To collect data, measure or observe one feature in a large sample, such as leaf length to the nearest mm, and record it in a tally table.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026