Variation, mutations and the Human Genome Project — Edexcel GCSE Biology
Causes of variation, mutations and their effects, characteristics controlled by many genes, and the Human Genome Project.
Revision notes
4 short notes, in the order of the specification. Each one in short:
Most phenotypic features, such as height, are the result of multiple genes rather than a single gene. Several genes work together to produce the feature, so it shows a wide range of values rather than a few clear categories. Only some characteristics, such as flower colour in pea plants, are controlled by a single gene.
Variation is the differences between individuals of the same species. It is caused by genes, the environment, or often a combination of both. Genetic variation comes from mutation and sexual reproduction, and environmental variation from conditions such as diet. Continuous variation, such as height, takes any value in a range; discontinuous variation, such as sex, has distinct categories.
A mutation is a change in the base sequence of DNA. There is usually extensive genetic variation within a population, and it arises through mutations. Most mutations have no effect on the phenotype, some have a small effect, and rarely a single mutation significantly affects the phenotype. So it is wrong to say that all mutations are harmful.
The Human Genome Project was an international project, completed in 2003, that identified the sequence of bases in human DNA and where the genes are. It can help find genes linked to inherited disorders and develop new treatments tailored to a person's genes. Concerns include worry about incurable diseases and keeping genetic information private.
Exam questions
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Quick check questions
State where genetic variation in a population comes from.
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Mutations (and sexual reproduction).
What is environmental variation?
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Different characteristics caused by an organism's environment (acquired characteristics).
What effect do most mutations have on the phenotype?
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No effect.
Give one possible medical use of the Human Genome Project.
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For example, identifying genes linked to inherited disorders so that people can be tested, or developing treatments.
Frequently asked questions
What causes variation in a species?
Variation is caused by genes, the environment, or a combination of both. Genetic variation comes from mutation and sexual reproduction, which give individuals different alleles, as with eye colour. Environmental variation is caused by conditions during life, such as diet, climate or injury; for example, plant height can be affected by light.
What is the difference between continuous and discontinuous variation?
In continuous variation, a feature can take any value within a range, such as height or mass, and the results are shown on a histogram. In discontinuous variation, a feature falls into distinct categories with nothing in between, such as sex or flower colour, and the results are shown on a bar chart.
Are all mutations harmful?
No, most mutations are not harmful. A mutation is a change in the base sequence of DNA, and most mutations have no effect on the phenotype. Some have a small effect, and only rarely does a single mutation significantly affect the phenotype. Mutations are the source of genetic variation within a population.
What was the Human Genome Project?
The Human Genome Project was an international research project to map the human genome. Completed in 2003, it identified the sequence of bases in human DNA and where the genes are. It can help find genes linked to inherited disorders, test people at risk and develop treatments tailored to a person's genes.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026