This free quiz has 10 real AQA A-level Biology exam questions on populations and the Hardy–Weinberg principle (19 marks, about 25 minutes). It marks itself: the Hardy–Weinberg calculations are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.7.2)
what a gene pool is, and the definition of a population
working out an allele frequency for a gene with three alleles
calculating the percentage of heterozygotes from phenotype data
calculating an allele frequency with the Hardy–Weinberg equation
estimating the number of individuals with a codominant phenotype
why observed phenotype frequencies can differ from those expected
when the Hardy–Weinberg equation can't be used, or the principle wouldn't hold
estimating how many people have a rare inherited condition
How to use it
Write each answer in full before you open the mark scheme, and show every step of your working in the calculations. Before you use the equation, write down which genotype or phenotype each figure in the question stands for. When you're asked for reasons, use the context: if the question says the population is large, its size isn't a reason.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Alleles in a gene pool. Fewer than half of students gained the mark. Common errors were writing genes instead of alleles, describing the frequency of an allele, or mentioning a species with no reference to a population.
✔ Gains credit: all the alleles in a population (alleles in a species alone was not enough).
Defining a population. 64% of students scored no mark in one paper. Many defined a community instead, or left out time.
✔ Gains credit: a group of organisms of the same species in a particular area at a particular time, that can interbreed to produce fertile offspring.
Why frequencies change. Almost four in five students scored zero in one question. Common wrong answers were crossing over, linked genes, codominance, independent segregation and random fertilisation.
✔ Gains credit: selection for or against a particular phenotype or allele, or mating that isn't random.
Say what is happening. Some students wrote the opposite of a credited point, such as “no mutation”, which was rejected. Many said the population was small even when the question stated it was large.
✔ Gains credit: a high rate of mutation, or immigration and emigration, so the population is not isolated.
When it can't be used. Most students said the allele was not known to be dominant or recessive, or that the allele frequency was unknown, and these were ignored. Some confused it with mark-release-recapture and wrote about no births or deaths.
✔ Gains credit: the condition is not caused by one gene, or environmental (including epigenetic) factors are involved, which Hardy–Weinberg cannot predict.
Percentage or frequency. Some students worked out the right value but gave it as a frequency (a decimal) when the question asked for a percentage, which lost a mark.
✔ Gains credit: the final answer as a percentage when the question asks for a percentage; the same value written as a frequency gained only one of the two marks.
Use every figure given. When estimating numbers from frequencies, a quarter of students lost a mark by leaving out one of the percentages in the information. An unrounded answer also lost a mark.
✔ Gains credit: applying every proportion given in turn, then rounding to the nearest whole number when the question asks for it.
Keep practising
The other AQA 3.7 self-marking quizzes: Inheritance · Evolution and speciation · Populations in ecosystems
Next, topic 3.8: the gene expression quiz
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.