Interpret a model of clone and mixed-genotype survival
Use specified stress responses to calculate survivors without turning a model into universal proof.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cells, DNA, inherited characteristics and the distinction between growth of an organism and production of offspring.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many of 100 genotype G plants survive at 20%?
What you will learn
- Calculate survival with the right group denominators
- Explain the genotype-specific model and its limits
Interpret a model of clone and mixed-genotype survival
Invented same-stress model: G survival 20%, H 80%. Uniform 100 G → 20 survivors; mixed 50 G + 50 H → 10 + 40 = 50. Difference 30 percentage points. Original teaching model.
| Group | Starting G | Starting H | Survivors |
|---|---|---|---|
| Uniform G | 100 | 0 | 20 |
| Mixed G/H | 50 | 50 | 50 |
| Feature | Meaning |
|---|---|
| Uniform group | 100 G; 20 survive |
| Mixed group | 50 G and 50 H; 10 + 40 survive |
| Comparison | 20% versus 50%; difference 30 percentage points |
| Limit | Stipulated stress responses; mixed-group origin unspecified |
Calculate survival with the right group denominators
The invented stress model compares 100 plants of genotype G with a second group containing 50 G and 50 H plants. Under the stated same exposure, 20% of G and 80% of H survive. The first group is a uniform clone lineage in the model; the second is a mixed-genotype group. The mixed group’s reproductive origin is not supplied, so do not assume its diversity must have arisen through one particular route.
The uniform group has 100 × 0.20 = 20 survivors. In the mixed group, G contributes 50 × 0.20 = 10 and H contributes 50 × 0.80 = 40, giving 50 survivors. Both starting totals are 100, so survival is 20% versus 50%, a difference of 30 percentage points. Genotype-specific response and the population survival percentage use different denominators.
Explain the genotype-specific model and its limits
In this model, including H allows more plants to survive the specified stress than the all-G group. The advantage depends on H being better suited to that stress; diversity is not a guarantee that some genotype resists every possible change. If both genotypes had the same supplied response, this particular numerical difference would disappear.
These are stipulated model outcomes, not repeated field observations proving causation or measured real-world survival thresholds. Exposure, genotype labels and survival fractions are assumptions here. The record illustrates a possible disadvantage of uniformity and a potential benefit of different inherited responses, while requiring a conditional conclusion rather than ranking every reproductive mode in every habitat.
Pause and explain
What supports the mixed group’s advantage in this model?
Worked example
Calculate mixed-group survivors from 50 G at 20% and 50 H at 80%.
Show the worked solution
- G survivors = 10.
- H survivors = 40; add both groups.
Answer 50 survivors from the 100 mixed-genotype plants.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Calculate survivors in uniform G and mixed G/H groups.
Give me a hint
Calculate each genotype contribution before adding.
Compare my reasoning
- Uniform: 100×0.20 = 20.
- Mixed: 50×0.20 + 50×0.80 = 50.
Uniform G: 20 survivors. Mixed G/H: 50 survivors.
Look for these in your work
- Use supplied fractions
- Add genotype contributions
Calculate survival percentages and their percentage-point difference.
Give me a hint
Both starting totals are 100.
Compare my reasoning
- Uniform survival = 20/100×100 = 20%.
- Mixed survival = 50/100×100 = 50%.
20% versus 50%; mixed group is 30 percentage points higher.
Look for these in your work
- Use original group denominators
- State percentage-point difference
Does this model prove that all mixed populations came from sexual reproduction and always survive better?
Give me a hint
Separate supplied genotype diversity from absent origin and other stresses.
Compare my reasoning
- The reproductive origin is not supplied.
- The advantage depends on the stated response to this stress.
No. Mixed-genotype origin is unspecified, and the advantage depends on H’s higher survival under this particular stress. It is not universal proof for every population or condition.
Look for these in your work
- Identify missing origin evidence
- Qualify the stress-specific conclusion
Common mistakes
- Averaging percentages without considering group sizes.
- Claiming every diverse population survives every stress.
What can you explain now?
What supports the mixed group’s advantage in this model?
Compare with the explanation
Genotype H has a higher supplied survival fraction for this stress
The conclusion is stress-specific.
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Make it stick
Calculate each genotype’s survivor contribution and explain why the conclusion is conditional on the supplied stress model.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.