Investigate pea seed shape and colour as separate discontinuous features
Use the mature-seed key and keep separate samples and features separate.
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
- Recall genes, alleles, genotype and phenotype from the inheritance pathway. Use the stated organism, units and sample; the records in these lessons are invented.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Are seed shape and seed colour the same feature?
What you will learn
- Classify supplied pea phenotypes consistently
- Describe frequencies without inventing joint records
Original teaching model. Measurements, categories, DNA fragments and comparison records are invented; assumptions and sample boundaries are stated.
| Feature | Meaning |
|---|---|
| Shape sample | 30 records: round 18 / wrinkled 12 |
| Shape percentages | 60% / 40% |
| Separate colour sample | 20 records: yellow 14 / green 6 |
| Joint shape–colour count | Not supplied by separate samples |
Classify supplied pea phenotypes consistently
Pea seed shape and pea seed colour are two required examples of discontinuous variation under their supplied phenotype keys. In the shape model, mature seeds are classified as round or wrinkled. In the colour model, the supplied categories are yellow or green. Examine the actual feature named in the task; a seed’s shape classification is not a measurement of its length and does not tell you which colour was recorded.
For the original shape dataset, thirty invented mature-seed records contain eighteen round and twelve wrinkled. The round proportion is eighteen divided by thirty, sixty per cent; wrinkled is forty per cent. A bar chart preserves two separate phenotype categories. This sample’s count ratio is eighteen to twelve, which reduces to three to two. Do not relabel it as a guaranteed Mendelian offspring ratio or identify parental genotypes without a supplied cross.
Describe frequencies without inventing joint records
A separate colour sample of twenty invented records contains fourteen yellow and six green, giving seventy and thirty per cent. Because these records are a separate sample, they do not tell you how many of the thirty shape specimens were both round and yellow. A joint investigation would record both features for the same identified specimens and use a shape–colour cross-tabulation, while keeping the original phenotype keys.
A safe practical plan uses clearly identified comparable mature specimens or supplied images with suitable keys, samples without selecting only one appearance, and records each valid specimen once. Damaged, immature or unclear specimens need a stated decision rule and an explicit unclassified count; do not silently force them into a category to improve a ratio. Observed category frequencies describe the valid sample. The written plan does not establish practical skill, parental genotype or a causal genetic mechanism for an unspecified specimen.
Sources for this lesson
Pause and explain
Can separate shape and colour samples identify the number both round and yellow?
Worked example
Describe shape frequencies for eighteen round and twelve wrinkled records, and decide whether the separate colour sample gives a round-and-yellow count.
Show the worked solution
- Check the shape total: 18 + 12 = 30, so frequencies are 60% round and 40% wrinkled.
- The colour records are a separate sample; no specimen-level pairing is supplied.
Answer Shape frequencies are 60% and 40%, with sample count ratio 3:2. A joint round-and-yellow count cannot be recovered from these separate samples.
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.
Find round and wrinkled percentages from 18 and 12 out of 30 records.
Give me a hint
Use the checked total 30.
Compare my reasoning
- 18/30 × 100 = 60%.
- 12/30 × 100 = 40%.
Round 60%; wrinkled 40%.
Look for these in your work
- Correct common denominator
- Both categories labelled
A separate twenty-record colour sample has 14 yellow and 6 green. Find percentages and the simplified sample ratio.
Give me a hint
This is the colour sample, not the thirty-record shape sample.
Compare my reasoning
- 14/20 × 100 = 70%; 6/20 × 100 = 30%.
- Reduce 14:6 by two.
Yellow 70%, green 30%; the observed colour ratio is 7:3.
Look for these in your work
- 20-record denominator
- Observed ratio distinguished from prediction
A class finds three damaged seeds in addition to its thirty valid shape records and removes them without mentioning them. Repair the report.
Give me a hint
Readers need to know which specimens were classifiable.
Compare my reasoning
- Report 33 examined, 30 validly classified and 3 unclassified under the damage rule.
- State whether percentages refer to the 30 valid records; do not infer the damaged specimens’ shapes.
Report the unclassified count and a 30-valid-record denominator for the stated shape percentages. Do not assign unsupported phenotypes to damaged seeds.
Look for these in your work
- Sampling and exclusion rule visible
- Correct valid-record denominator
Common mistakes
- Applying a shape count to a separate colour sample
- Calling an observed 3:2 ratio a guaranteed cross prediction
- Ignoring unclear or damaged specimens
What can you explain now?
Can separate shape and colour samples identify the number both round and yellow?
Compare with the explanation
No; joint records are missing
Both features must be recorded on the same specimens.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, classify supplied pea phenotypes consistently and describe frequencies without inventing joint records. Keep units, the stated sample and the limits of the evidence clear.
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.