AQA GCSE Combined Science (8464), Higher tier · Biology › Inheritance, variation and evolution › Variation and evolution
Practise Variation. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Variation is the differences in characteristics between individuals, caused by genes, the environment or both. You need to know that all genetic variants arise from mutations and how the genome and the environment together shape the phenotype. It is often tested with data on twins or plants grown in different conditions.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Define variationDifferences in the characteristics of individuals in a population.
4
Classify causes of variationGenetic (genes inherited), environmental (conditions of development) or a combination of both.
5
Give examples of each causeBlood group is genetic, a scar is environmental, and body mass depends on both.
5
State that populations show genetic variationThere is usually extensive genetic variation within a population of a species.
6
Describe how mutations affect phenotypeAll variants arise from mutations: most have no effect on the phenotype, some influence it and very few determine it.
7
Use twin or clone dataIdentical twins and clones have the same genes, so differences between them are caused by the environment.
7
Explain how a mutation can change a speciesA rare new phenotype that suits an environmental change can spread relatively quickly by natural selection.
Notes
Causes of variation
Variation is the differences in the characteristics of individuals in a population.
It may be due to differences in the genes they have inherited (genetic causes), the conditions in which they have developed (environmental causes), or a combination of genes and the environment.
Environmental examples: a scar, the language you speak, a plant's leaves turning yellow because of a lack of light.
Both: human height and body mass; the height of a plant, which depends on its genes and on light, water and mineral ions.
Your genome sets what is possible; your environment affects how those genes develop into your phenotype.
Mutations and variants
There is usually extensive genetic variation within a population of a species.
All genetic variants arise from mutations, which occur continuously.
Most variants have no effect on the phenotype; some influence the phenotype; very few determine the phenotype.
Very rarely a mutation leads to a new phenotype. If the new phenotype suits a change in the environment, it can lead to a relatively rapid change in the species.
Separating genes from environment
Identical twins have the same genes, so any differences between them are caused by the environment.
Non-identical twins have different genes, so they usually differ more.
In plants, grow genetically identical plants (clones) in different conditions: any differences must be caused by the environment.
Cheatsheet
Variation = differences in the characteristics of individuals in a population
Causes: genetic, environmental, or a combination
Genome + environment → phenotype
There is usually extensive genetic variation within a population
All variants arise from mutations; mutations occur continuously
Most mutations have no effect on the phenotype; some influence it; very few determine it
A rare new phenotype suited to an environmental change → relatively rapid change in the species
Identical twins have the same genes, so their differences are environmental
How to answer each type of question
Classify variation as genetic, environmental or both
1 to 3 marks4
Ask: can this change during life because of conditions? If yes, the environment plays a part.
Ask: is it inherited? If yes, genes play a part.
Most measurable features, such as height and mass, are caused by both.
Example. Give the cause of each of these types of variation: genetic, environmental or both. (a) A person's blood group (b) A scar on a person's arm (c) A person's body mass [3 marks]
Show the model answer
(a) Genetic (1) (b) Environmental (1) (c) Both (1)
Explain the role of mutations
2 to 3 marks6
All variants arise from mutations.
Most have no effect, some influence and very few determine the phenotype.
A rare new phenotype can spread quickly if it suits a change in the environment.
Example. Mutations happen all the time, but most mutations do not change an organism's phenotype. Explain how a mutation can occasionally lead to a rapid change in a species. [3 marks]
Show the model answer
Very rarely a mutation produces a new phenotype (1). If the environment changes and the new phenotype is suited to the new conditions, those individuals are more likely to survive and reproduce (1). So the allele is passed on and becomes common in the population relatively quickly (1).
Use twin or clone data
2 to 4 marks7
State that identical twins (or clones) have identical genes.
So any differences between them must be caused by the environment.
Compare with non-identical twins: bigger differences show that genes also play a part.
Quote numbers from the data.
Example. Scientists measured the difference in body mass between the two people in pairs of adult twins. Identical twins: mean difference 4.1 kg. Non-identical twins: mean difference 9.6 kg. What do these results suggest about the causes of variation in body mass? Explain your answer. [3 marks]
Show the model answer
Identical twins have the same genes, so their 4.1 kg difference must be caused by the environment, e.g. diet or exercise (1). Non-identical twins differ more (9.6 kg) because they also have different genes (1). So body mass is affected by both genes and the environment (1).
Shortcuts and memory tricks
Mutation effects from most to fewest: no effect → influence → determine (most, some, very few).
Could it change during your life? Then the environment plays a part.
Twins test: identical twins have the same genes, so any difference is environmental.
Where marks are lost
Saying variation is only caused by genes. Many characteristics depend on both genes and the environment.
Saying mutations are always harmful. Most have no effect on the phenotype.
Saying identical twins have no variation. They can differ because of their environment.
Classifying height or body mass as purely genetic.
Exam technique
In data questions, quote numbers and say what they show about genes compared with the environment.
Use the words genotype, phenotype and environment accurately.
When explaining a rapid change in a species, link mutation → new phenotype → suits a changed environment → natural selection.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Body mass is affected by both genes and the environment. Give one environmental factor that affects body mass.
Diet / amount of exercise
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Differences in the characteristics of individuals in a population are called variation.
(a) Which characteristic is caused only by genetic factors? Tick (✓) one box.[1]
Blood group
Body mass
Language spoken
A scar on the knee
(b) Which characteristic is caused only by the environment? Tick (✓) one box.[1]
Blood group
Eye colour
Height
A tattoo
(c) Body mass is affected by both genes and the environment. Give one environmental factor that affects body mass.[1]
(d) All genetic variants arise in the same way. What causes genetic variants?[1]
(e) Which statement about genetic variants is correct? Tick (✓) one box.[1]
Most genetic variants determine the phenotype
Most genetic variants have no effect on the phenotype
Most genetic variants are harmful
Most genetic variants are useful
Show the answer and mark scheme
(a)Answer: Blood group
(b)Answer: A tattoo
(c)Answer: Diet / amount of exercise
diet / amount of food eaten / exercise
(d)Answer: Mutations
mutation(s)
(e)Answer: Most genetic variants have no effect on the phenotype
Question 2Medium5 marks
Variation between individuals can be caused by genes, by the environment, or by a combination of both.
(a) Classify each characteristic as caused mainly by genes, mainly by the environment, or by a combination of both. Natural hair colour .......... The language a person speaks .......... Height ..........[3]
(b) Two plants were grown from seeds produced by the same two parent plants. They were grown in the same greenhouse, but one plant grew much taller than the other. Suggest two reasons for this difference.[2]
Show the answer and mark scheme
(a)Answer: Genes; environment; a combination of both
natural hair colour: genes
the language a person speaks: environment
height: a combination of both
(b)Answer: The seeds were produced by sexual reproduction, so the plants inherited different alleles; and one plant may have had more light, water or mineral ions than the other
genetic: the seeds were produced by sexual reproduction, so the plants inherited different alleles / different combinations of genes for height
environmental: one plant may have received more light / water / mineral ions (e.g. because of its position in the greenhouse)
Question 3Hard4 marks
Variation between individuals is essential for both natural selection and selective breeding.
(a) Explain why a population with very little genetic variation would respond poorly to natural selection if the environment changed suddenly.[2]
(b) Explain why a population with very little genetic variation would also be of limited use to a breeder trying to improve a characteristic by selective breeding.[2]
Show the answer and mark scheme
(a)Answer: Natural selection relies on some individuals being better suited to the changed conditions than others; with little variation there is little difference between individuals, so few may be well suited to the new conditions
natural selection relies on some individuals being better suited to survive changed conditions than others
with little variation there is little difference between individuals, so few (or none) may be well suited to the new conditions, risking a large population decline
(b)Answer: A breeder selects individuals with the most desirable version of a characteristic to breed from; with little variation there is little difference to select between, so progress would be very slow
a breeder selects individuals with the most desirable version of a characteristic to breed from
with little variation there is little difference to select between, so progress towards an improved characteristic would be very slow or impossible