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.

1. (a)(i)Table 2.1 shows the possible genotypes of the Patty pan and Alfresco varieties. Complete Table 2.1 to show the possible genotypes of the Di Nizza variety.[1]
2. (a)(ii)A gardener used pollen from a male flower of Alfresco to pollinate a female flower of Di Nizza. The gardener grew the seeds produced from this cross and found that half the offspring produced spherical fruits and half produced long fruits. Draw one genetic diagram to explain this result. parent genotypes gametes offspring genotypes offspring phenotypes[4]
3. (a)(iii)The offspring show genetic variation with respect to fruit shape alleles. Name the process that occurred during meiosis in the parents that produced this variation and state the stage of meiosis at which it occurred. process stage of meiosis[2]
4. (b)(i)Genetically modified (GM) summer squash plants with resistance to viral diseases have been grown in the USA since 1995. Scientists have been concerned that viral resistance genes pass easily from GM squash plants to their wild relative, the Texas gourd, Cucurbita texana. Explain why the possibility of gene flow from GM squash plants to the Texas gourd is a cause of social and environmental concern. social environmental[2]
5. (b)(ii)A study compared the survival of two different types of hybrids that were formed by cross-pollination between GM virus-resistant squash plants and wild Texas gourd plants: virus-resistant hybrids that had inherited the viral resistance gene non-resistant hybrids that had not inherited the viral resistance gene. Viral disease outbreaks caused many of the non-resistant hybrids to die. Leaf-eating beetles then moved in larger numbers to the surviving healthy virus-resistant hybrids. The beetles carried a pathogenic bacterium Erwinia which was capable of killing the plants. [Figure 2.2] compares infection with Erwinia in the virus-resistant hybrids and the non-resistant hybrids. Discuss whether these results provide support for the use of genetically modified organisms (GMOs) in food production.[2]
6. (b)(iii)Suggest why the GM virus-resistant squashes grown by farmers rarely suffer infection by Erwinia.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.