Interpret phenotype records across generations
Keep sample sizes and denominators visible; phenotype shares are not automatically allele frequencies.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Use the stated case, sample and assumptions. Diagrams and numerical records in this pathway are original teaching models; written answers are self-checked.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why retain both sample counts and percentages?
What you will learn
- Calculate comparable phenotype proportions
- State whether records support a generational trend
Original selection schematic. Population counts and scenarios are supplied teaching models; they are not field observations.
| Stage or record | Meaning |
|---|---|
| Generation A | 18/60 = 30% |
| Generation B | 32/80 = 40% |
| Denominators | 60 and 80 recorded plants |
| Limit | Phenotype proportion, not allele frequency |
Calculate comparable phenotype proportions
Population records can show how common an observed feature is at different times. Compare the same phenotype definition and stage in each generation. If 18 of 60 plants show a feature in one cohort, the proportion is 18/60 = 30%. If 32 of 80 show it later, the proportion is 40%. Report the denominator as well as the percentage.
Sample size matters. A small sample may vary by chance, and samples taken from different places or ages may not represent the same population. A graph with percentages alone can hide different denominators. Check how individuals were sampled, how a generation was defined and whether the same measurement rule was used.
State whether records support a generational trend
Phenotype frequencies and allele frequencies are different quantities. One phenotype may arise from more than one genotype; some genotypes may share a phenotype. Without genotype counts and a justified inheritance model, do not call a phenotype percentage an allele percentage. The syllabus requirement is about adaptation over generations, not an unstated population-genetics calculation.
Even comparable phenotype proportions do not prove natural selection caused a trend. Evidence for inherited variation and differential reproduction helps connect the pattern to the mechanism. Other factors such as migration, mutation, sampling or changed conditions could also matter. State a supported observation first, then the mechanism only if the data justify it.
Sources for this lesson
Pause and explain
What do 18/60 and 32/80 show?
Worked example
Generation A has 18 of 60 plants with the feature; Generation B has 32 of 80. Calculate both percentages and compare their denominators.
Show the worked solution
- Calculate 18/60 and 32/80 separately.
- The proportions are 30% and 40%; the cohort sizes differ.
Answer The recorded feature share rises from 30% to 40%. Generation A has 60 plants and Generation B 80; the percentages do not by themselves prove natural selection or measure allele frequencies.
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 and compare 24/80 and 21/60.
Give me a hint
Use the denominator belonging to each cohort.
Compare my reasoning
- 24/80 = 0.30 = 30%.
- 21/60 = 0.35 = 35%.
The recorded proportions are 30% and 35%; report 80 and 60 as the sample sizes.
Look for these in your work
- Both percentages
- Cohort sizes retained
A graph reports feature frequency 25%, 50%, 45% across three generations with sample sizes 20, 100 and 22. Describe the pattern cautiously.
Give me a hint
State the sequence and note the uneven cohort sizes.
Compare my reasoning
- The percentage rises and then falls.
- The sample sizes differ greatly, so uncertainty in the small groups may be larger.
The recorded proportion rises from 25% to 50% then falls to 45%; uneven sample sizes and other study details limit claims about the whole population.
Look for these in your work
- Trend described
- Sampling caution
A dominant phenotype is seen in 70% of a cohort, but no genotypes are provided. Can the allele share be calculated as 70%? Explain.
Give me a hint
One phenotype can correspond to more than one genotype.
Compare my reasoning
- The 70% is an observed phenotype proportion.
- Genotype counts and a justified inheritance model are missing.
No. The record gives a phenotype share; without genotype data and explicit assumptions it does not give the allele frequency.
Look for these in your work
- Correct quantity
- Evidence needed
Common mistakes
- Ignoring unequal sample sizes
- Confusing phenotype with allele frequency
- Inferring a cause from two samples alone
What can you explain now?
What do 18/60 and 32/80 show?
Compare with the explanation
30% then 40% of the recorded cohorts
The calculations use each cohort’s own denominator.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, calculate comparable phenotype proportions and state whether records support a generational trend. Explain the mechanism, use the given population or breeding records and state what the evidence does not establish.
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.