The Relationship between the Genotype and Phenotype of Drosophila melanogaster Eye Pigment
T.A: Zahra Mortaji
Our TLC plate showed all colours expressed by the pteridine pigments for the wild-type Drosophila as expected (Figure 1). The sample A mutant which was a bright-red eye mutant also expressed the same pigments as our wild-type. Compared to the wild type, sample A pigment spots were lower intensity in colour under the UV light (Figure 2). Sample B was a brown-eye phenotype that showed no pigments except for a very faint 2-amino-4-hydroxypterin pigment (Figure 2). This was probably the result of human error because it was expected that there would be no pigments shown on the TLC plate for the brown-eye mutant. Furthermore, sample C which was the white-eyed mutant where no pigments were expected; however, our actual results did not reflect this. Instead our TLC plate faintly expressed Isoxanthopterin (violet-blue) for the white eye mutant (Figure 2). This was most likely due to human error. Moreover, the pigments found for sample D which was the dark-brown grey phenotype were: Isosepiapterin, Biopterin, 2-amino-4-hydroxypterin, and Isoxanthopterin and was lacking Sepiapterin, Xanthopterin, and Drosopterin (Figure 1). The Sepiapterin and Xanthopterin pigment was expected to show on the TLC plate (Figure 1) but unfortunately our plate did not reflect this. Again, this could be due to human error during the experiment. The Rf values for the pteridine pigment spots were similar for both the wild type and mutants of Drosophila. The wild type and sample A (bright-red eye mutant) had very similar Rf values for all the pigments (Table 1). Conversely, the Rf values for Isosepiapterin, Isoxanthopterin and Sepiapterin for the wild-type were slightly higher than those same pigments of sample A (Table 1). The 2-amino-4-hydroxypterin spot for sample B (Brown-eye) was close in value to the other 2-amino-4-hydroxypterin spots. It was also the highest in value compared to the others (Table 1). There were no Rf values for the rest of the pigments as they were not present for sample B. Similarly sample C (white-eye) had only one Rf value as only one pigment (Isosepiapterin) was expressed. The pigment Isosepiapterin for sample C was close in value to its counterparts as well, but in this case it was the lowest in value compared to the other Isosepiapterin pigments (Table 1). Sample D had very similar Rf values to both the wild type and sample A as expected (Table 1). However, the pigments Sepiapterin, Xanthopterin, and Drosopterin were lacking so there were no Rf values for those pigments for sample D. Discussion:
Our control group for this experiment was the wild-type Drosophila which does not have mutations in either the pterdinine or ommochrome pathway. The phenotypes were found by direct observation where the flies’ eye colour were viewed under a stereomicroscope. However, the genotype was found by chromatography of eye pigments. This was done by isolating eye pigments on a TLC plate. By comparing the pigments of the mutant’s eye colour to the wild-type we were able to determine the genotypes present. The wild-type has the complete set of pteridine pigments, where the mutation may be lacking in certain pigments this can help us determine which enzyme or pathway is not functioning properly in a mutant. For example the wild type shows all the pteridine pigments where the white eye mutant does not show them: this indicates that there is an enzyme or transporter that is not functioning as it should. The white eye mutant is a mutant because it has a mutation that does not allow the pigments to be transported. Although, our actual results showed a faint Isoxanthopterin pigment (Figure 2) this is due to human error that has occurred during the course of the experiment. Thus, based on the genotypes presence and functioning of certain...
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