Fruit Fly Lab Report

The mode of inheritance for the four traits of eye shape, eye color, bristle morphology, and body color were studied in Drosophila melanogaster, or commonly known as the fruit fly. Each gene was analyzed through reciprocal crosses of wild type alleles and mutant alleles in the flies. The gene for body color encodes either a honey yellow or ebony color in the fly. It was determined that the honey, which is the wild type, is the dominant allele and the ebony color is the recessive allele. Eye color, eye shape, and bristle morphology were all determined to be sex linked on the X chromosome as they are more prevalent in the males. If these genes were found on the Y chromosome, there would be no females found with mutations in the eye shape, eye

As seen in Figure 1, the linkage map displays the map units and the order of the eye shape, eye color, and bristle type genes. In order to determine the distance between the genes, map units must be calculated, which can be found in Table 5. The calculations were performed by adding together the recombinants of the parents and dividing by the total number of flies counted and multiplying that by 100. This was done for each of the genes in order to identify which of the three genes was in the middle. Determination of the middle gene allowed for the relative positions of the other two genes to be calculated. Bristle morphology was determined to be in the center of the other two as it is the gene that switches in the recombinants. Bar eyes was calculated to be the first gene on the X chromosome 47.0 map units away from the middle gene bristle morphology. Eye color was found to be 17.7 map units from the middle bristle morphology gene, and 64.7 map units away from the bar eye gene, making it the last of the three genes on the X chromosome. The body color gene was already found to be on a separate chromosome. Therefore, it is not linked to eye color, eye shape, or bristle morphology that were found to be on the X

The cross of BWSE X ++++ were found to be BWS+. Female F1 were found to be B+++ for the cross of ++++ X BSWE and for the cross of BWSE X ++++. The absence of an ebony body color in both the male and female F1s corresponds with the recessiveness of this allele. Bar eye can be observed in the females due to the distance between the linked genes. There is a higher chance of the eye shape allele of the chromosome to switch as this section is 47.0 map units away from the bristle morphology and even further from the eye color. The body color gene in the F2 data was analyzed using a chi square test to see if the it fit the expected 3:1 Mendelian ratio. There were 168 honey body colored flies observed in the F2 data, and 47 ebony body colored flies. These two numbers were compared to expected values for a 3:1 ratio in order to obtain the X2 value of 1.213. The degree of freedom was determined to be 1 for the data, which is necessary for the interpretation of the X2 value. Using the degree of freedom and the X2 value, a corresponding p-value of 0.2710 was determined. This p-value is above the Alpha value of 0.05 indicating that the data does not differ significantly from the 3:1 ratio. In addition this p value greater than 0.05 implies that any observed deviation is obtained by chance alone, specifically between 20% and 30% of the time. Therefore, the null hypothesis of the F2 data fitting the expected Mendelian 3:1 ratio