Genetics & Evolution: A Level Biology questions and answers
10 free A Level Biology Genetics & Evolution questions written in the style of Cambridge Biology papers, each with its answer and mark scheme. 4 of them are A* challenge questions, built to catch the mistakes strong students still make.
This topic covers Inheritance, Selection & evolution, Classification, biodiversity & conservation, Genetic technology. Work through the questions below, then generate a full Genetics & Evolution paper with a fresh set every time.
The numbers of individuals of four species found in a quadrat survey were 30, 10, 5, 3.
(a)
Calculate Simpson’s index of diversity, D = 1 − Σ(n/N)2.
[3]
(b)
In a mark–release–recapture study, 40 beetles were marked; later 45 were caught, of which 10 were marked. Estimate the population size and state two assumptions.
[4]
(c)
Explain why conserving biodiversity is important.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
0.551
N = 48 B1 Σ(n/N)2 calculated M1 0.551 A1
3
(b)
180; no migration/births/deaths, marks not lost, marking does not affect survival, random mixing
c1 × c2 ÷ m M1 180 A1 two valid assumptions B2
4
(c)
ecological stability/food webs; source of drugs/genes; economic (tourism) and ethical reasons
any three valid reasons B3
3
Question 2Structured · 3 marksA* challenge
The Hardy–Weinberg principle estimates allele frequencies.
In a population, 16% of individuals show a recessive phenotype. Calculate the frequency of heterozygotes.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
0.48
q² = 0.16 so q = 0.4 C1 p = 0.6 C1 2pq = 0.48 A1
3
Question 3Structured · 11 marksA* challenge
(a)
Describe how the polymerase chain reaction (PCR) amplifies a DNA sequence.
[4]
(b)
Calculate the number of copies after 25 cycles starting from one molecule, and explain why the real number is lower.
[2]
(c)
Describe how gel electrophoresis separates DNA fragments.
[3]
(d)
Discuss one benefit and one concern of genetically modified crops.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
denature at 95 °C separating strands; anneal primers at ~55 °C; extension by Taq polymerase at 72 °C; cycle repeated, doubling each cycle
denaturation ~95 °C B1 primers anneal ~55 °C B1 Taq (thermostable) polymerase extends at ~72 °C B1 repeated cycles; exponential amplification B1
4
(b)
225 ≈ 3.4 × 107; reagents (primers, nucleotides) run out / enzyme efficiency falls
3.4 × 107B1 limited reagents/efficiency B1
2
(c)
DNA negatively charged (phosphate); moves towards anode through agarose gel; smaller fragments move further
DNA negatively charged B1 moves towards positive electrode B1 smaller fragments travel further B1
3
(d)
benefit: herbicide/pest resistance, higher yield, vitamin A (Golden Rice); concern: gene transfer to wild relatives, reduced biodiversity, superweeds
valid benefit B1 valid concern B1
2
Question 4Structured · 4 marksA* challenge
Meiosis produces genetic variation.
Explain how crossing over and independent assortment produce variation.
[4]
Show answers and mark scheme
Part
Answer and marking points
Marks
exchange between chromatids; random orientation of pairs
crossing over at chiasmata in prophase I B1 exchanges alleles between non-sister chromatids B1 independent assortment: random orientation of homologous pairs at metaphase I B1 produces different combinations of alleles B1
4
Question 5Structured · 3 marks
In a population, 24% of individuals show a recessive phenotype. Use the Hardy–Weinberg principle to calculate the frequency of heterozygous individuals.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
0.5
q = √q2C1 p = 1 − q C1 0.5 A1
3
Question 6Structured · 8 marks
This question is about the tools of genetic technology.
(a)
Explain the roles of restriction enzymes and DNA ligase.
[3]
(b)
Explain why reverse transcriptase is used to make the insulin gene for insertion into bacteria.
[2]
(c)
Explain why PCR is useful in forensic science.
[2]
(d)
State one use of bioinformatics in genetic technology.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
cut at specific recognition sequences; sticky ends; ligase joins sugar–phosphate backbones
restriction enzymes cut DNA at specific base sequences B1 often producing complementary sticky ends B1 DNA ligase forms phosphodiester bonds to join fragments B1
3
(b)
mRNA from beta cells has no introns; bacteria cannot remove introns
mRNA from pancreatic β cells is used to make cDNA without introns B1 bacteria cannot splice introns out of a eukaryotic gene B1
2
(c)
amplifies tiny samples; enough DNA for profiling
PCR makes many copies from a tiny sample of DNA B1 providing enough for electrophoresis / DNA profiling B1
2
(d)
storing and comparing sequence databases
storing, searching and comparing DNA and protein sequence databases B1
1
Question 7Structured · 9 marks
A student investigates whether the number of plant species in a quadrat is related to distance from a footpath.
distance from path / m
2
4
6
8
10
12
number of species
5
6
9
8
12
14
Table 7.1
(a)
State a null hypothesis for this investigation.
[1]
(b)
Calculate Spearman’s rank correlation coefficient for these data.
[3]
(c)
The critical value at p = 0.05 for n = 6 is 0.886. State the conclusion.
[2]
(d)
Describe how the student should sample species along a line transect from the path.
[2]
(e)
Explain why Spearman’s rank was chosen rather than Pearson’s correlation coefficient.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
no correlation between distance and number of species
there is no correlation between distance from the path and the number of species B1
1
(b)
0.943
ranks assigned to both variables M1 Σd2 = 2 M1 rs = 1 − 6Σd2/(n(n2 − 1)) = 0.943 A1
3
(c)
significant positive correlation; reject null
|rs| > 0.886 so the correlation is significant B1 reject the null hypothesis (species number increases with distance from the path) B1
2
(d)
quadrats at regular intervals along a tape from the path; record species in each
lay a tape at right angles to the path B1 place quadrats at regular intervals along it and record the number of species in each B1
2
(e)
data not normally distributed / relationship not linear
the data may not be normally distributed / the relationship is not expected to be linear (ignore: small sample) B1
1
Question 8Structured · 4 marks
Natural selection can lead to speciation.
Explain how allopatric speciation occurs.
[4]
Show answers and mark scheme
Part
Answer and marking points
Marks
geographical isolation; different selection pressures; reproductive isolation
populations separated by a geographical barrier B1 no gene flow B1 different mutations and selection pressures change allele frequencies B1 populations become reproductively isolated B1
4
Question 9Structured · 13 marks
This question is about gene technology.
(a)
Describe the polymerase chain reaction (PCR).
[4]
(b)
Explain why Taq polymerase is used.
[1]
(c)
Explain how gel electrophoresis separates DNA fragments.
[3]
(d)
Describe how genetic engineering produces human insulin using bacteria, including how transformed bacteria are identified.
[5]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
denature at 95 °C; anneal primers 55 °C; extend at 72 °C with Taq polymerase; repeat, doubling DNA each cycle
heat to about 95 °C to separate the DNA strands B1 cool to about 55 °C so primers anneal B1 heat to about 72 °C so Taq polymerase adds nucleotides B1 repeat cycles, doubling the DNA each time B1
4
(b)
thermostable, not denatured at 95 °C
thermostable: not denatured at 95 °C (optimum about 72 °C), so it survives each heating cycle (ignore: from thermophilic bacteria on its own) B1
1
(c)
DNA negatively charged (phosphate); moves towards anode; smaller fragments move faster through gel
DNA is negatively charged due to phosphate groups B1 moves towards the positive electrode B1 smaller fragments move further through the gel in a given time B1
3
(d)
mRNA → cDNA by reverse transcriptase; sticky ends, restriction enzyme; ligase into plasmid; transformation; marker gene e.g. fluorescent / antibiotic resistance
insulin mRNA used to make cDNA with reverse transcriptase B1 plasmid cut with a restriction enzyme leaving sticky ends B1 DNA ligase inserts the gene into the plasmid B1 plasmids taken up by bacteria (transformation, e.g. heat shock) B1 bacteria containing the recombinant plasmid identified using a marker gene (e.g. fluorescence / antibiotic resistance) B1
5
Question 10Structured · 9 marks
This question is about molecular evidence for evolution.
(a)
State what is meant by a species, using the biological species concept.
[2]
(b)
Explain how comparing DNA sequences can show how closely related two species are.
[2]
(c)
Explain why mitochondrial DNA is useful in tracing human evolution.
[3]
(d)
Describe one other type of molecular evidence used to compare species.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
group that can interbreed to produce fertile offspring; reproductively isolated from others
a group of organisms that can interbreed to produce fertile offspring B1 and are reproductively isolated from other such groups B1
2
(b)
more similar sequence = more recent common ancestor
the more similar the base sequences, the more recently the species shared a common ancestor (fewer mutations accumulated) B2
2
(c)
inherited only from mother; no recombination; mutates at steady rate (molecular clock)
mitochondrial DNA is inherited only through the mother B1 it does not undergo recombination B1 it accumulates mutations at a fairly constant rate, acting as a molecular clock B1
3
(d)
amino acid sequences of proteins such as cytochrome c / haemoglobin
comparing amino acid sequences of a common protein (e.g. cytochrome c) B1 fewer differences indicates closer relationship B1
In the 9700 syllabus, Genetics & Evolution covers Inheritance, Selection & evolution, Classification, biodiversity & conservation, Genetic technology.
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Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in