Investigate invented ABO phenotype counts without inferring population genotypes
Categorical counts need a total, clear labels and a stated sample.
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 denominator gives a sample phenotype percentage?
What you will learn
- Describe a discontinuous sample distribution
- Calculate labelled phenotype frequencies with evidence limits
Original teaching model. Measurements, categories, DNA fragments and comparison records are invented; assumptions and sample boundaries are stated.
| Feature | Meaning |
|---|---|
| Total records | 60 fictional phenotypes |
| Counts | A 24 / B 18 / AB 6 / O 12 |
| Percentages | 40% / 30% / 10% / 20% |
| Inference limit | Sample phenotype counts do not identify all genotypes |
Describe a discontinuous sample distribution
The original anonymised teaching dataset contains sixty invented ABO phenotype records: twenty-four A, eighteen B, six AB and twelve O. These are fictional data, not student medical results or a recommendation to test anyone’s blood. The common-model categories are distinct, so a bar chart gives each category a labelled bar with a gap between it and the next category. The horizontal order is a presentation choice rather than a continuous biological scale.
Add the counts to check the sample denominator: twenty-four plus eighteen plus six plus twelve equals sixty. A phenotype percentage is its count divided by sixty times one hundred. This gives A forty per cent, B thirty per cent, AB ten per cent and O twenty per cent. The counts sum to sixty and the percentages sum to one hundred, which checks the arithmetic but does not prove that the sample represents a wider population.
Calculate labelled phenotype frequencies with evidence limits
A is the most frequent phenotype in these records. That statement concerns the sample, not every region or age group. A sample intentionally selected to include particular groups can distort an estimate of a population distribution. The supplied phenotype counts also do not identify all genotypes: A could correspond to IAIA or IAIo and B to IBIB or IBIo in the common inheritance model.
Investigate discontinuous variation by classifying a supplied safe record set with a defined key, tallying each valid record once and describing the category frequencies. Do not average the arbitrary category names or interpret the four bars as body measurements. A separate genotype investigation would require appropriate additional evidence. Written handling of invented records is not clinical testing, consent for private data collection or supervised practical certification.
Sources for this lesson
Pause and explain
Can the 24 A phenotype records all be identified as IAIA from these counts alone?
Worked example
Calculate the proportion of phenotype AB in the sixty invented records.
Show the worked solution
- The AB count is 6 and the checked total is 24 + 18 + 6 + 12 = 60.
- Compute 6/60 × 100 = 10%.
Answer AB represents 10% of the invented sample; this does not establish a population-wide frequency.
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 the percentages of A and AB in the supplied sixty-record sample.
Give me a hint
Divide each count by the same checked total.
Compare my reasoning
- Calculate 24/60 × 100 for A.
- Calculate 6/60 × 100 for AB.
A is 40% and AB is 10% of this invented sample.
Look for these in your work
- Same 60-record denominator
- Both percentages labelled
Find the B and O percentages, then check all four percentages sum correctly.
Give me a hint
Use counts 18 and 12 with the total 60.
Compare my reasoning
- B = 18/60 × 100 = 30%; O = 12/60 × 100 = 20%.
- Combine with A 40% and AB 10% to obtain 100%.
B 30%, O 20%; all four sum to 100%.
Look for these in your work
- Correct B and O arithmetic
- Total percentage check
A researcher selects exactly sixty fictional records to obtain this chart and claims it proves regional ABO frequencies and every A genotype. Evaluate both claims.
Give me a hint
Sampling and phenotype ambiguity are different limits.
Compare my reasoning
- A selected record set need not represent the region.
- A phenotype can be IAIA or IAIo in the common model.
Neither claim follows: the chart describes its invented sample, and A phenotype counts cannot distinguish the two common A genotypes.
Look for these in your work
- Sampling limit
- Genotype ambiguity
Common mistakes
- Using only two categories in the denominator
- Inferring IAIA from every A phenotype
- Treating invented data as medical records
What can you explain now?
Can the 24 A phenotype records all be identified as IAIA from these counts alone?
Compare with the explanation
No; A also permits IAIo
Phenotype counts leave common-model genotype ambiguity.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Without your notes, describe a discontinuous sample distribution and calculate labelled phenotype frequencies with evidence limits. 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.