(a) The fruit fly, Drosophila melanogaster, feeds on sugars found in damaged fruits. A fruit fly with normal features is described as wild type. It has red eyes and its wings are longer than its abdomen. There are mutant variations such as purple eyes or short (vestigial) wings. Fig. 7.1 shows a wild type fruit fly and a mutant fruit fly with purple eyes and vestigial wings. [Figure 7.1] • The genes coding for eye colour and wing length are located on the same chromosome. • Allele R for red eyes is dominant to allele r for purple eyes. • Allele N for long wings is dominant to allele n for vestigial wings. (b) A wild type fruit fly, heterozygous for both genes, was crossed with a fruit fly that was homozygous recessive for both genes.

1. (a)Explain what is meant by the terms allele and dominant. allele dominant[2]
2. (b)(i)Table 7.1 is a summary of the cross. Complete Table 7.1. Table 7.1 wild type parent | double homozygous recessive parent ---|--- parental | phenotype | X parental | genotype | X offspring | [Diagrams of four offspring phenotypes: red eye, long wing; purple eye, vestigial wing; red eye, vestigial wing; purple eye, long wing] offspring | phenotype | offspring | genotype | number of | 1339 | 1195 | 151 | 154 offspring[5]
3. (b)(ii)Explain why the four offspring phenotypes are not present in a 1:1:1:1 ratio.[3]

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.