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5.1 Inheritance

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Question 1

In a species of sweet pea, flower colour is determined by a biochemical pathway controlled by two independently assorting genes, A A\,A and BBB:

Colorless Precursor 1→Enzyme AColorless Precursor 2→Enzyme BRed Pigment \text{Colorless Precursor 1} \xrightarrow{\text{Enzyme A}} \text{Colorless Precursor 2} \xrightarrow{\text{Enzyme B}} \text{Red Pigment} Colorless Precursor 1Enzyme A​Colorless Precursor 2Enzyme B​Red Pigment
  • Enzyme A is coded for by the dominant allele AAA. The recessive allele a a\,a produces a non-functional enzyme.
  • Enzyme B is coded for by the dominant allele BBB. The recessive allele b b\,b produces a non-functional enzyme.

If two plants heterozygous for both genes (AaBbAaBbAaBb) are crossed, what is the expected phenotypic ratio of red-flowered to white-flowered offspring?

A

9:3:3:19:3:3:19:3:3:1

B

12:3:112:3:112:3:1

C

9:79:79:7

D

9:3:49:3:49:3:4

Markscheme

5.1 Inheritance Questions

  1. GCSE
  2. /Biology
  3. /5.1 Inheritance

97 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.

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