FreeScienceLessons · AQA BiologyVariation — genetic and environmental
Key facts
Types of variation
Continuous variation — a range of values with no distinct categories. Examples: height, weight, foot size, intelligence.
Discontinuous variation — distinct categories with no intermediate values. Examples: blood group (A, B, AB, O), tongue rolling, sex (male/female).
Continuous variation shown on a bar or line graph/histogram.
Discontinuous variation shown on a bar chart.
Causes of variation
Genetic variation — differences in DNA/alleles. Caused by mutation, meiosis (crossing over, independent assortment), sexual reproduction.
Environmental variation — caused by conditions during growth (nutrition, sunlight, disease). Identical twins differ due to environmental factors.
Both genetic and environmental — most traits are influenced by both. Height is genetic but also affected by nutrition.
Mutations — random changes in DNA sequence. Usually neutral, occasionally harmful, rarely beneficial.
Exam questions — 3 questions · 9 marks
⚡ Extended questions included. Read the hint. Write in full sentences. AI marks against the AQA mark scheme.
1 markContinuous variationAQA 8461 style
Which of the following is an example of continuous variation?
A Blood group
B Ability to roll tongue
C Height
D Sex
1 markMutation causeAQA 8461 style
What causes a genetic mutation?
A Environmental factors only — mutations are always caused by radiation or chemicals
B A random change in the DNA base sequence
C Crossing over of chromosomes during mitosis
D Inheritance of alleles from parents
4 marksExplain why variation is important for evolutionAQA 8461 P2 style
Explain why variation within a species is necessary for evolution by natural selection to occur. (4 marks)
Hint: Cover: variation exists → some traits are better adapted → those individuals survive and reproduce → pass on alleles → frequency increases over generations.