Features controlled by multiple genesSpec 3.19
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.
Some characteristics, like flower colour in Mendel's pea plants, are controlled by a single gene. These are the ones used in monohybrid crosses.
Most phenotypic features are the result of multiple genes rather than single gene inheritance. Several genes work together to produce the feature. Features controlled by many genes, such as height, show a wide range of values rather than a few clear categories.
Exam tip:If a question asks why a feature does not follow a simple 3 : 1 ratio, one answer is that it is controlled by more than one gene.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026
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.
All 4 questions on Variation, mutations and the Human Genome Project
