Eye Colour Genetics in Fruit Flies Lab
Bio 1210 R02
In this Lab we studied how different variations in eye colour for fruit flies, Drosophila melanogaster, are produced. We looked at flies with brick red eyes, white eyes, and sepia eyes. To determine whether or not the gene was autosomal or sex-linked we did reciprocal crosses for brick red eyes with white eyes and brick red eyes with sepia eyes. Both female and male versions of brick red eye colour were tested with white and sepia which also had male and female flies used for testing.
Our predictions for brick red-eyed female crossed with a white-eyed male had a phenotypic ratio of all red eyes. In our results we had 44 females and 11 males with red eyes. No white eyes were seen for male or female. Our predictions were also the same for white-eyed female crossed with a red-eyed male, with a phenotype of all red eyes. This time our predictions were not correct; eight white-eyed males were seen in the petri dish. Since white-eyed males are seen with this reciprocal cross this gene is sex-linked. Only males have the mutant white-eyed gene on the X chromosome. For females to have the mutant eye colour both X chromosomes need to be affected with the gene. In our second predictions for reciprocal crosses we had brick red female with sepia male and sepia female with brick red male. We predicted a phenotypic ratio of all red eyes. In our results this was true. No sepia-eyed male or female fruit flies were recorded. This suggest that the gene is autosomal. The sepia eye colour is not present in either the X or Y chromosome meaning the allele would have to be located on an autosome.
The biochemical pathway was responsible for different eye colour pigments in the fruit flies. When both males and females only contain red eyes, enzyme one converted purine riboside into an intermediate compound. The non-functional enzyme was enzyme three which would lead to the sepia pigment. To get a white-eyed fruit fly like we...