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Secondary Biology: Inheritance and Mendel (Paper 2)
Secondary Biology: Inheritance and Mendel (Paper 2)
Ten original questions on 3:1 and 1:1 counts, using a test cross to tell TT from Tt, the 1:2:1 ratio under incomplete dominance and multiplying probabilities.
Direct answer Write the parental genotypes first. A test cross uses the recessive homozygote, and independent events multiply.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: Secondary Biology: Inheritance and Mendel |
| Level | 4 basic, 3 advanced, 2 challenge and 1 redo question |
02 Questions (10 items)
- FoundationTt is crossed with Tt and 800 seeds are sown. About how many are tall?
- FoundationTt is crossed with tt and 500 offspring are expected. How many are tall and how many short?
- FoundationWhat are the genotypes and phenotypes of the offspring of TT crossed with tt?
- FoundationHow many chromosomes does a human gamete carry?
- IntermediateA tall plant is test-crossed with a short one, giving 96 tall and 92 short offspring. What is the genotype of the tall parent?
- IntermediateWith incomplete dominance, RW is crossed with RW and 400 offspring are produced. What is the expected split?
- IntermediateA couple plans two children. What is the chance both are boys, and how many of 400 two-child families would that be?
- ChallengeHow can a test cross tell whether a tall plant is TT or Tt?
- ChallengeHow do genotype and phenotype differ, and why do they not always map one to one?
- Error redoA pupil claims a 3:1 ratio must appear in every experiment. Is that right?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | About 600 (200 short, a 3:1 ratio). | The 3:1 ratio is expected, so multiply the total by three quarters. |
| 2 | 250 of each, a 1:1 ratio. | A cross with the recessive homozygote gives a 1:1 ratio. |
| 3 | All are Tt and all are tall. | Each offspring receives one allele from each parent. |
| 4 | 23, half the 46 found in body cells. | Meiosis separates the pairs, so gametes are haploid. |
| 5 | Tt, because the near 1:1 ratio shows it can pass on a t allele. | A TT parent would give only tall offspring in a test cross. |
| 6 | 100 red, 200 pink and 100 white, a 1:2:1 ratio. | With incomplete dominance the heterozygote shows an intermediate phenotype. |
| 7 | One in four (1/2 times 1/2), about 100 families. | Each birth is independent, so the probabilities multiply. |
| 8 | Cross it with tt: all-tall offspring means TT, while a near 1:1 ratio means Tt. | The tester parent must be the recessive homozygote. |
| 9 | Genotype is the allele combination (TT, Tt, tt); phenotype is the observable feature. TT and Tt look the same but differ in genotype. | One phenotype can come from more than one genotype. |
| 10 | No. It is an expected ratio; small samples vary, so 20 seeds might give 14 to 6. | The larger the sample, the closer the result comes to the expected ratio. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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