The patty pan squash plant, Cucurbita pepo, produces edible fruits that vary in colour. (a) The colour of the fruits is controlled by two genes, A/a and B/b, that occur on different chromosomes. • Allele A produces a white fruit colour. • Allele a does not produce a colour by itself but allows the colours coded by gene B/b to show in the phenotype. • Allele B produces a yellow fruit colour. • Allele b produces a green fruit colour. In a dihybrid cross, an AABB plant was crossed with an aabb plant. All the resulting F1 plants produced white fruits. The F1 plants were then crossed with each other to obtain the F2 generation.

1. (a)(i)Complete Fig. 2.1 with the gametes produced by the F1 parents, the F2 genotypes and the F2 phenotypes. State the ratio of fruit colours in the F2 offspring. F1 parents: AaBb x AaBb [Figure 2.1][4]
2. (a)(ii)Test crosses were carried out on two white-fruited plants, P and Q, from the F2 generation. Each of these plants had its female flowers pollinated with pollen from a green-fruited plant. For plant P, half of the offspring were white and half were yellow. For plant Q, half of the offspring were white and half were green. Deduce the genotypes of plants P and Q. plant P plant Q[2]
3. (a)(iii)Plants P and Q show genetic variation with respect to fruit colour alleles. Identify the process that occurred during meiosis in the F1 parents that produced this variation and the stage of meiosis at which it occurred. process stage of meiosis[2]
4. (b)(i)In 1994, two new varieties of squash were grown in the USA. Both varieties showed resistance to two viral diseases of squash plants. • The variety 'Tigress' was developed by selective breeding. • The variety 'Freedom II' was developed by adding genes for viral coat proteins to the squash genome. Identify, with reasons, the variety of squash that can be described as recombinant.[2]
5. (b)(ii)Outline one social advantage and one social disadvantage of the recombinant squash variety compared to non-resistant squash varieties. advantage disadvantage[2]

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