AQA GCSE Biology Biology Paper 2 (Foundation), June 2024: Question 8
8 marks · Standard Demand difficulty · Short Answer
Use genetic crosses and Punnett squares to determine genotypes, phenotypes, and offspring ratios in pea plants, and explain why Mendel's work on inheritance was initially not accepted.
Practise this questionQuestion
Question text
08 In 1866, a monk called Gregor Mendel published the results of his investigations into
inheritance in pea plants.
Pea plants produce seeds in a pod.
Figure 9 shows a pea pod.
Figure 9
Pea seeds can be round or wrinkled in shape.
Mendel crossed pea plants that produced round seeds with pea plants that produced
wrinkled seeds.
Figure 10 shows the results.
Figure 10
In questions 08.1 to 08.3 use the following symbols to represent the alleles:
R = dominant allele for round seeds
r = recessive allele for wrinkled seeds.
*0328*1
. In Figure 10, the genotype of plant 1 is RR.
Give the genotype of plant 2.
[1 mark]
Mendel collected the seeds from plants 3 and 4 and grew new plants from the seeds.
Mendel crossed the new plants.
08.2 Complete the Punnett square diagram in Figure 11.
You should show:
• the male gametes
• the offspring genotypes.
[3 marks]
Figure 11
08.3 Give the ratio of round seeds to wrinkled seeds in the offspring in Figure 11.
[1 mark]
Ratio of round seeds to wrinkled seeds =34 :
08.4 Some of the offspring in Figure 11 are homozygous and some are heterozygous.
*33* What does ‘heterozygous’ mean?
[1 mark]
08.5 Mendel published his work in 1866.
Suggest two reasons why the importance of Mendel’s work was not recognised until
the early 1900s.
[2 marks]
Mark scheme
Show the mark scheme
Question 8
AO /
Question Answers Extra information Mark
Spec Ref.
08.1 r r allow homozygous recessive 1 AO2
4.6.1.6
AO /
Spec Ref.
08.2 male gametes correct: R and r 1 AO2
4.6.1.6
all four offspring genotypes allow 1 mark for 2 or 3 correct 2
correctly derived from gametes
(given)
AO /
Spec Ref.
08.3 correct ratio from Figure 11 allow 3 : 1 if no answer to 08.2 1 AO3
4.6.1.6
AO /
Spec Ref.
08.4 having (two) different alleles (of ignore example(s) 1 AO1
a gene) do not accept having– two – – 4.6.1.6
different genes
AO /
Spec Ref.
08.5 any two from: 2 AO2
4.6.3.3
• other scientists not aware of allow work lost for many years
his work or work published in
obscure journal
• other theories accepted at the allow eg theory of blending
time inheritance
ignore religion
• not considered to be a allow he was only a monk
scientist or not eminent or not allow he was not believed
respected
• Mendel’s (mathematical) allow his work was not
approach was novel concept understood or no other scientist
had similar ideas
allow his results were not
corroborated (at the time)
• peas gave unusual results allow Mendel only worked on
compared with other species pea plants
allow insufficient results /
research
• new discoveries made allow specific discoveries
Mendel’s work relevant
Total Question 8 8
How to answer it
Gregor Mendel & Monohybrid Crosses: Pea Plants
This question assesses fundamental genetics knowledge and historical understanding from Topic 4.6 (Inheritance, Variation and Evolution). You need to deduce parental genotypes, complete a monohybrid Punnett square cross, determine phenotypic ratios, define key genetic terminology ( heterozygous ), and explain why revolutionary scientific discoveries are not always recognised immediately.
Genotype of Plant 2
Deducing the genotype for a recessive phenotype
✅ Correct Answer
rr
Also allowed: homozygous recessive .
💡 Key Knowledge
- Dominant alleles ( R ) show their effect even if only one copy is present.
- Recessive alleles ( r ) only show their phenotype when homozygous ( rr ).
- Because Plant 2 has wrinkled seeds (the recessive trait), its genotype must be double recessive.
❌ Common Errors
- Writing a single allele like r instead of a pair of alleles ( rr ).
- Mixing up capital and lowercase letters (e.g. writing Rr , which would produce round seeds).
🧠 Exam Technique
A genotype represents a pair of alleles in a diploid organism. Always write two letters unless specifically asked for a gamete!
Completing the Punnett Square
Crossing two heterozygous F1 plants (Plant 3 × Plant 4)
✅ Completed Punnett Square
| Female | |||
|---|---|---|---|
| R | r | ||
| Male | R | RR | Rr |
| r | Rr | rr |
🧠 Step-by-Step Breakdown
- Step 1 (Parent Genotypes): Both parents (plants 3 and 4) were produced from RR × rr , so all F1 plants are heterozygous ( Rr ).
- Step 2 (Gametes): The female gametes are already given ( R and r ). Fill the male row headers with the same: R and r . [1 Mark]
- Step 3 (Offspring): Cross row by column to complete the 4 internal boxes: RR , Rr , Rr , rr . [2 Marks for all 4; 1 Mark for 2 or 3 correct]
Phenotype Ratio
Calculating the ratio of round to wrinkled seeds
✅ Correct Answer
3 : 1
Round seeds : Wrinkled seeds = 3 : 1
📐 Step-by-Step Working
- Count round phenotypes ( RR , Rr , Rr ) = 3
- Count wrinkled phenotypes ( rr ) = 1
- Write as a simplified ratio: 3 : 1
❌ Common Errors
- Reversing the numbers: Writing 1 : 3 loses the mark because the question asked for round : wrinkled. Check the order requested!
- Giving genotype ratios: Writing 1 : 2 : 1 gives the genotype ratio ( RR : Rr : rr ), not the requested phenotype ratio.
Definition of 'Heterozygous'
Biological terminology recall
✅ Correct Answer
Having two different alleles (of a gene).
💡 Allele vs Gene
- Gene: A small section of DNA that codes for a specific protein / characteristic (e.g. seed shape gene).
- Allele: A different version or variant of that same gene (e.g. R for round, r for wrinkled).
❌ Major Mark-Loser
Do NOT write "having two different genes". Examiners strictly reject this! A heterozygous organism has one gene, but two different alleles for that gene.
Historical Context: Why Was Mendel Ignored?
Understanding the acceptance of scientific ideas
✅ Any TWO of the following reasons:
- Lack of awareness: Mendel published his paper in an obscure, local scientific journal; other scientists were unaware of his work (or the work was "lost" for decades).
- Conflicting theories: Other theories were widely accepted at the time (e.g. the idea of "blended inheritance").
- Lack of scientific status: Mendel was an Augustinian monk, not an established or respected university scientist.
- Unfamiliar mathematical approach: His use of statistics and mathematical ratios in biology was novel and poorly understood.
- Mechanism unknown: Chromosomes, genes, and DNA had not yet been discovered or observed in cell division (meiosis).
🧠 Exam Technique
- Be precise: Don't just say "people didn't like him". Say "he was not considered an eminent scientist" or "he was an unknown monk".
- Avoid religious claims: Do not write that "religion banned it" or "the Church stopped him" — the mark scheme explicitly states: ignore religion.
- Give two distinct points on separate numbered lines.
Topics
Biology · B6: Inheritance, Variation and Evolution
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Foundation), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.