OCR A 6.1.2 · 20 written questions · 47 marks · about 55 minutes · marked as you go
This free quiz has 20 written exam questions on patterns of inheritance, all taken from OCR A Level Biology A papers (A level, 2018 to 2025, plus OCR practice or sample papers). Short answers mark themselves. For longer answers you write your answer, then tick off the OCR mark-scheme points you made, so you see exactly where the marks are. The quiz covers variation, genetic diagrams and sex linkage, linkage and epistasis, the chi-squared test, bottlenecks and the Hardy–Weinberg principle, speciation and artificial selection.
What the quiz covers (OCR A spec 6.1.2)
Variation (6.1.2(a), (d)): genetic and environmental causes of variation, why sexual reproduction is useful in harsh conditions, and continuous versus discontinuous variation.
Genetic diagrams and sex linkage (6.1.2(b)(i)): dihybrid crosses, multiple alleles on a Z chromosome, sex determination in birds and mammals, and reading a family tree.
Linkage and epistasis (6.1.2(b)(ii)): what an unexpected dihybrid ratio tells you and how one gene can affect another gene's expression.
The chi-squared test (6.1.2(c)): calculating χ², finding the critical value and writing a conclusion.
Evolution and allele frequencies (6.1.2(e)–(f)): genetic bottlenecks and a Hardy–Weinberg calculation.
Speciation and artificial selection (6.1.2(g)–(h)): the conditions needed for speciation, inbreeding in dog breeds and why breed welfare needs managing.
How to use it
Write every answer in full, as you would in the exam: the mark for each question is shown, so you know how much to write. When you self-mark, only tick a point if your answer clearly makes it, then read the examiner's tip under each question. Your progress is saved on your device, so you can do it in two sittings, and at the end you can retry just the questions where you dropped marks.
Prefer multiple choice? Try the 12-question Genetics and Evolution multiple choice quiz first.
Open the Patterns of Inheritance quiz in a new tab (easier on a phone)
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Linked genes share a chromosome: Explaining an unexpected dihybrid ratio with sex linkage, codominance or epistasis, or writing 'the alleles are linked', which OCR ignored.
✔ Gains credit: Autosomal linkage: the two genes are on the same chromosome, so there is no independent assortment and the alleles are inherited together.
Link epistasis to the phenotype: Stopping at 'one gene masks another' and not saying what that does to the offspring.
✔ Gains credit: The product of one gene masks the expression of another gene, so the phenotype is affected by more than one gene and the ratio changes.
Gametes carry one allele per gene: Writing AA, Aa or Bb as gametes, or giving gametes (AB, ab) when the question asks for a parent's genotype.
✔ Gains credit: A parent with genotype AaBb makes the gametes AB, Ab, aB and ab: one allele of each gene.
Not every dihybrid is 9:3:3:1: Writing down 9 : 3 : 3 : 1 out of habit when only one parent is a double heterozygote.
✔ Gains credit: Work out each parent's gametes, complete a Punnett square and count each phenotype, matching each phenotype to its number in the ratio.
Expected values come from the null hypothesis: Getting the expected values wrong in a χ² calculation: this was the most common error.
✔ Gains credit: If the null hypothesis says there is no effect, the expected value is the total shared equally between the categories.
Significant difference, not significant data: Calling the 'results' or 'data' significant.
✔ Gains credit: The difference between the observed and expected results is significant, with less than a 5% probability that it is due to chance, so the null hypothesis is rejected.
Degrees of freedom: categories minus one: Reading the critical value from the wrong row of the χ² table.
✔ Gains credit: Degrees of freedom = number of categories − 1; then read across to the p = 0.05 column.
Only males, so think X: Linking a disease that only affects males to the Y chromosome, or writing 'males are more likely to have it'.
✔ Gains credit: The allele is recessive and on the X chromosome: only males have the disease, and healthy parents have affected sons.
Keep practising
Try the Genetics and Evolution multiple choice quiz, the Cell Division multiple choice quiz, the Cellular Control written quiz or the Manipulating Genomes written quiz, or browse all our OCR A Level Biology quizzes. Our OCR A masterclasses (Year 12 on Wednesdays at 5.15pm, Year 13 on Tuesdays at 6.30pm) work through real exam questions on one topic each week.
Questions, mark schemes and examiners' report extracts © OCR.