The summer squash plant, Cucurbita pepo, produces edible fruits that vary in shape. [Figure 2.1] shows the fruits of three different varieties of squash plants. Fruit shape in squashes is controlled by two genes, A/a and B/b, that are located on different chromosomes. A disc-shaped fruit is produced when both dominant alleles, A and B, are present. A spherical fruit is produced when either allele A or allele B is present, but not if both A and B are present. A long fruit is produced when both allele A and allele B are absent.

Q: What topic does this question test?

This question tests Inherited change in A-Level Biology (syllabus code 9700). It is worth 12 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Biology May/June 2020 examination, Paper 4 Variant 2 (9700_s20_qp_42.pdf).

Question

The summer squash plant, Cucurbita pepo, produces edible fruits that vary in shape. [Figure 2.1] shows the fruits of three different varieties of squash plants. Fruit shape in squashes is controlled by two genes, A/a and B/b, that are located on different chromosomes. A disc-shaped fruit is produced when both dominant alleles, A and B, are present. A spherical fruit is produced when either allele A or allele B is present, but not if both A and B are present. A long fruit is produced when both allele A and allele B are absent.

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