Variation
Practise Variation for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Variation can be genetic, environmental or a combination of both, and it provides the raw material for natural selection.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Variation means the differences between individuals of the same species. It arises from genes, from the environment, or from a combination of both.
Genetic variation comes from the alleles inherited from the parents. Environmental variation comes from the conditions in which an organism has developed. Most variation is caused by a combination — height, for example, is influenced by inherited genes but also by diet.
All variation ultimately arises from mutations, which are random changes to the DNA. Most have no effect on the phenotype, some influence it slightly, and very rarely a mutation determines the phenotype and may lead to a new characteristic.
Revision notes
Sources of variation
Genetic: differences in the alleles inherited from the parents.
Environmental: differences caused by the conditions the organism has grown in, such as diet or light availability. Combined: most characteristics are influenced by both.
Mutations
Mutations are random changes to the DNA, and they occur continuously.
Most have no effect on the phenotype. Some influence it slightly. Very rarely, a single mutation determines the phenotype and produces a new characteristic.
Variation and natural selection
There is usually extensive genetic variation within a population of a species.
If a new characteristic makes an individual better suited to the environment, it can lead to rapid change in the species through natural selection.
Key points
- Variation is the difference between individuals of a species.
- Variation may be genetic, environmental or both.
- Most variation is caused by a combination of genes and environment.
- All genetic variation arises from mutation.
- Most mutations have no effect on the phenotype.
- Rarely a mutation produces a new characteristic.
Worked examples
Example 1
Give one example of a characteristic influenced by both genes and the environment, and explain your answer. [2 marks]
Model answer
Height (1 mark). A person inherits genes influencing how tall they can grow, but their actual height also depends on environmental factors such as diet during childhood (1 mark).
Example 2
Explain what a mutation is and describe its usual effect on the phenotype. [3 marks]
Model answer
A mutation is a random change to the DNA (1 mark). Most mutations have no effect on the phenotype (1 mark), although a few influence it slightly and very rarely one determines the phenotype entirely (1 mark).
Example 3
Explain how variation can lead to rapid change in a species. [2 marks]
Model answer
If a mutation produces a new characteristic that makes an individual better suited to its environment (1 mark), that individual is more likely to survive and reproduce, passing the characteristic on, so the species changes rapidly through natural selection (1 mark).
Common mistakes
Saying all mutations are harmful.
Most have no effect at all; only a few are significant, and some are beneficial.
Saying mutations happen because an organism needs them.
They are random and are not directed by need.
Giving only genetic causes of variation.
Environmental factors and combinations of both are also required.
Confusing variation with evolution.
Variation is the differences present; evolution is the change over generations.
Exam tips
- Give an example that clearly involves both genes and environment.
- Say mutations are random changes to the DNA.
- Emphasise that most mutations have no effect.
- Link beneficial mutations to natural selection.
Key terms
- Variation
- Differences between individuals of the same species.
- Mutation
- A random change to the DNA.
- Phenotype
- The characteristics actually expressed by an organism.
- Allele
- A different form of a gene.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.