Turn over 9 4 Fruit flies, Drosophila melanogaster, are often used in genetics investigations. The diagrams show male and female flies. Female Male Actual size = 3 mm (a) Give one feature, visible in the diagrams, that you could use to distinguish between male and female flies and state how it differs between them. (1) Feature .................................................................................................................................................................................................................................................................................... Difference .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) A scientist investigated the inheritance of several genes in fruit flies. (i) A grey-bodied fly was crossed with a black-bodied fly. All the offspring in the F1 generation were grey-bodied. Two of the grey-bodied flies from the F1 generation were then crossed. Determine the expected ratio of phenotypes of the offspring in the resulting F2 generation by using a genetic diagram. (2) Answer .......................................................................................................................................................... 10 (ii) Normal fruit flies have long wings but some flies have very short wings called vestigial wings. The allele for long wing (L) is dominant to the allele for vestigial wing (l). The gene for wing length is located on chromosome 2. The allele for normal antennae (A) is dominant to the allele for bushy antennae (a). The gene for antennae shape is located on chromosome 3. Two flies which are heterozygous for both characteristics are crossed. Determine the ratio of phenotypes that you would expect in the next generation, using a genetic diagram. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Turn over 11 (iii) The allele for red eyes (R) is dominant to the allele for white eyes (r). The scientist investigated the inheritance of eye colour. The crosses used were: cross 1 – a red-eyed female fly was crossed with a white-eyed male fly: half of the offspring were red-eyed females and half were red-eyed males cross 2 – a white-eyed female fly was crossed with a red-eyed male fly: half of the offspring were red-eyed females and half were white-eyed males. Explain the results of these crosses. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 4 = 10 marks)