These eight questions move from naming terms to drawing a cross to judging a claim. Try each one on paper before opening the answer.
The set covers the cluster on genetics. The timed practice session builder can turn it into a timed run.
Questions
Question 1 (2 marks). Arrange these in order from the smallest to the largest: chromosome, gene, nucleus.
Answer
Gene, chromosome, nucleus. A gene is a section of DNA, chromosomes carry many genes, and the nucleus contains the chromosomes.
Question 2 (2 marks). State what DNA is, and what a gene is.
Answer
DNA is the chemical that stores genetic information. A gene is one section of DNA that carries the instruction for one characteristic.
Question 3 (2 marks). A plant has genotype Rr, where R is the dominant allele for round seeds. Write the gametes it can produce.
Answer
R and r. Each gamete carries one allele only, so the gametes are single letters.
Question 4 (4 marks). Two round-seeded plants, both Rr, are crossed. Complete the grid and state the genotype and phenotype ratios.
Answer
Grid boxes: RR, Rr, Rr, rr.
Genotype ratio: 1 RR : 2 Rr : 1 rr. Phenotype ratio: 3 round : 1 wrinkled, because RR and Rr both show round seeds.
Question 5 (3 marks). The cross in Question 4 produces 200 seeds. State the expected number of wrinkled seeds, and explain why the real count may differ.
Answer
Wrinkled is 1 in 4, so the expected number is 200 ÷ 4 = 50.
The ratio is an expected pattern. Which gametes meet is a matter of chance, so the real count may be a little different.
Question 6 (3 marks). A cross between Rr and rr is made. State the expected phenotype ratio.
Answer
Gametes: R and r from the first parent, r only from the second. Offspring: 2 Rr : 2 rr.
The ratio is 1 round : 1 wrinkled.
Question 7 (3 marks). Two identical twin sisters grow up in different towns. One is 3 cm taller than the other. Explain the difference.
Answer
Identical twins share the same genes, so genes cannot explain the difference. The cause is the environment, for example a difference in diet or exercise during growth.
For non-identical siblings, different combinations of alleles could also contribute.
Question 8 (4 marks). A fictional study finds that 60 of 80 plants with variant M are pest-resistant, while 20 of 80 plants without M are resistant. A student writes “Variant M makes plants pest-resistant.” Rewrite the conclusion so it fits the data.
Answer
With M, 60 ÷ 80 = 75% are resistant. Without M, 20 ÷ 80 = 25%.
Careful conclusion: “Plants with variant M were more likely to be pest-resistant (75% compared with 25%), so M is linked to resistance. Since 20 of 80 plants with M were not resistant, other factors may also matter.”
If you got these wrong
- Questions 1 and 2: revisit distinguishing genes, chromosomes and DNA.
- Questions 3 to 6: work through completing basic inheritance diagrams.
- Question 7: read explaining variation with examples.
- Question 8: see interpreting genetic information without deterministic claims.
A mistake log helps you track the repeat errors. If you want a teacher to read your written answers, see online one-to-one Science tuition.