Flowers of the common morning-glory plant, Ipomoea purpurea, can have several different
phenotypes. An example of these flowers is shown in Fig. 3.1.
[Figure 3.1]
Flower colour in I. purpurea is controlled by two genes on different chromosomes.
Gene R/r, which codes for a protein involved in pigment production, has 2 alleles:
•
the dominant allele, R, allows pigment production
:
the recessive allele, r, prevents pigment production of any colour, resulting in white flowers.
Gene T/t, which determines the type of pigment produced, has two alleles:
:
the dominant allele, T, results in purple flowers
the recessive allele, t, results in red flowers.

Q: What topic does this question test?

This question tests Inherited change in A-Level Biology (syllabus code 9700). It is worth 10 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Biology Feb/Mar 2020 examination, Paper 4 Variant 2 (9700_m20_qp_42.pdf).

Question

Flowers of the common morning-glory plant, Ipomoea purpurea, can have several different
phenotypes. An example of these flowers is shown in Fig. 3.1.
[Figure 3.1]
Flower colour in I. purpurea is controlled by two genes on different chromosomes.
Gene R/r, which codes for a protein involved in pigment production, has 2 alleles:
•
the dominant allele, R, allows pigment production
:
the recessive allele, r, prevents pigment production of any colour, resulting in white flowers.
Gene T/t, which determines the type of pigment produced, has two alleles:
:
the dominant allele, T, results in purple flowers
the recessive allele, t, results in red flowers.

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