Connect all eight Core variation requirements using measurements categories and genetic-change evidence
A complete explanation distinguishes phenotype patterns, causes, investigation and mutation.
Section B17.1 · Variation
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
What should come first in a variation explanation?
What you will learn
- Connect continuous and discontinuous variation with investigations
- Explain genetic change new alleles and mutation-rate conditions
Original teaching model. Measurements, categories, DNA fragments and comparison records are invented; assumptions and sample boundaries are stated.
| Feature | Meaning |
|---|---|
| Continuous examples | Body length / body mass |
| Discontinuous examples | ABO / supplied pea shape / supplied pea colour |
| Investigation | Consistent key, sample, units and denominator |
| Mutation | Genetic change; new alleles; rate relationship |
Connect continuous and discontinuous variation with investigations
Begin with individuals of the same species and a clearly named phenotype feature. Body length and body mass illustrate continuous variation: measurements can lie across a range between extremes. Common-model ABO categories, pea seed shape and pea seed colour illustrate discontinuous variation: a supplied phenotype key defines a limited set of categories without intermediates. Instrument rounding and arbitrary category codes do not change the underlying biological distinction.
The syllabus’s usual cause pattern is genes only for discontinuous variation and both genes and environment for continuous variation. Retain usually and the supplied model. A visible growth change alone does not establish mutation, and a shared phenotype alone does not prove identical genotypes. A descriptive sample can show variation without isolating its genetic and environmental contributions.
Explain genetic change new alleles and mutation-rate conditions
A sound written investigation defines same-species comparable specimens, a sampling frame and a consistent measurement or category protocol. Record valid observations once, retain repeated readings as repeats, explain exclusions and name units and denominators. The twenty invented pod lengths occupy classes 4, 7, 6 and 3, while a separate seed record or ABO record uses its own total. A histogram of adjoining equal-width length intervals differs from separated bars for named phenotypes.
Mutation is genetic change and is the way new alleles form in the syllabus account. Ionising radiation and some chemicals increase mutation rate; this is not a directed beneficial change or a guarantee for every organism. These lessons give original teaching and self-checked guided, independent and application practice for all eight Core requirements. The Supplement adds gene-mutation detail and four genetic-variation sources.
Sources for this lesson
Pause and explain
Which summary preserves the syllabus’s usual causes?
Worked example
Connect the twenty-pod histogram, a round/wrinkled seed sample and the supplied DNA fragment change.
Show the worked solution
- Length intervals describe a continuous measurement with a checked twenty-specimen total; seed-shape bars describe supplied discontinuous categories.
- The same-locus DNA sequence change establishes a genetic difference in its stipulated record, while body measurements alone do not.
Answer Classify the phenotype structure, preserve each sample’s protocol and denominator, and distinguish genetic-change evidence from growth observations.
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.
Classify body length, body mass, common ABO phenotype, mature pea seed shape and seed colour under their supplied models.
Give me a hint
Separate measured ranges from category keys.
Compare my reasoning
- Length and mass allow intermediate measurements.
- ABO, shape and colour use the supplied limited phenotype categories.
Length and mass are continuous; common ABO, round/wrinkled shape and yellow/green colour are discontinuous under the supplied models.
Look for these in your work
- All five examples
- Model limits retained
The twenty pod records have class counts 4, 7, 6 and 3. The separate seed sample has 18 round out of 30. Find the second length-class percentage and round-seed percentage.
Give me a hint
Use each dataset’s own total.
Compare my reasoning
- Second length class: 7/20 × 100 = 35%.
- Round seeds: 18/30 × 100 = 60%.
35% in the 50–<60 mm length class and 60% round in the separate seed sample.
Look for these in your work
- Both correct denominators
- Percentages and features labelled
Explain why the supplied changed DNA fragment can be genetic-change evidence, whereas water-related growth and completing this pathway do not establish a new allele or a practical grade.
Give me a hint
Separate sequence evidence, phenotype observations and assessment approval.
Compare my reasoning
- A stated same-locus DNA alteration supports genetic change; a length response alone does not supply that alteration.
- Written self-checking does not provide human teacher review, supervised practical competence or cumulative assessment.
The fragment supports its stipulated genetic change. Growth alone does not demonstrate a new allele, and completing written lessons does not establish teacher approval, practical competence or a whole-qualification grade.
Look for these in your work
- Genetic versus phenotype evidence
- Assessment limits explicit
Common mistakes
- Treating one sample total as every dataset’s denominator
- Equating visible variation with mutation
- Treating mapped teaching as teacher or practical approval
What can you explain now?
Which summary preserves the syllabus’s usual causes?
Compare with the explanation
Discontinuous usually genes only; continuous genes and environment
This keeps the required distinction and the word usually.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, connect continuous and discontinuous variation with investigations and explain genetic change new alleles and mutation-rate conditions. 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.