Model organism Drosophila melanogaster, commonly referred to as the fruit fly, is a low-cost option with a few unique characteristics that make it an excellent tool for a variety of scientific investigations. In genetic investigations, Drosophila melanogaster models are favoured over vertebrate counterparts because of the flies' simple dietary needs, rapid reproduction capacity, and short life cycle. Depending on factors like food and stress, it can live up to a maximum of 120 days on average. In addition to being simple and affordable to produce, they also take up very little room in a laboratory.
They also exhibit a wide range of readily apparent phenotypic characteristics. The compound eye and other anatomical traits make it simple to perform phenotypic characterizations on this species. Despite their relatively tiny genome, they exhibit a wide range of genetic diversity. In just four chromosomes, there are around 13,600 coding genes for proteins. These flies allow researchers to look at a wide range of genetic variants. There are several examples of this, such as the Drosophila gene that codes for eye colour, which can result in either red, sepia or white eye colour. D. melanogaster is a useful research tool for studying the link between genotype and phenotype because of its capacity to develop a wide variety of phenotypes.
When D. melanogaster parents with different wild-type and mutant phenotypes of eye colour and wing size mated, we wanted to see what kind of offspring they would have. Sepia and white are the two most common mutations in eye colour, although red is the most common wild type. When it comes to wing size, the wild type has lengthy wings, but the mutant has no wings at all. When we looked at the phenotypic ratios, we anticipated that the Mendelian Law of Segregation applied to one variable, and we were eager to find out why. Using D. melanogaster flies of various phenotypes, we tested whether or not our findings were in accordance with Mendelian Law of Segregation, which states that comparable phenotypes do not breed together. As a result, two monohybrid crossings were made: one in which both the male and female flies had the wild type phenotype (Bb and Bb), and another in which both male and female flies had the mutant phenotype (XwY) (X+X+).
We sought to test Mendel's first law by crossing wildtype red-eyed flies to see what the predicted phenotypic ratio would be. Mendelian law dictates that the two alleles are segregated during gamete production, thus we projected that the expected phenotypic ratio for a hybrid with red-eye flies would be 3:1. This time around, we wanted to know how many red-eyed flies and white-eyed flies would be predicted to cross in our previous monohybrid cross, according to Mendel's first law. Due to the Mendelian Law of Segregation, we predicted that the phenotypic ratio would be 1:1. We will be ready to reject or fail to reject our hypothesis based on the findings of our mating cross using the chi-square test.
As a group of two, students were allocated a specific fly stock vial number. Before class began, students gathered at the front of the room to receive two culture vials already prepared with food and cotton plugs. The vials were labelled with the study group's number and initials. After that, the cotton plugs in the allocated stock vials were gently tapped on the lab bench to eliminate any flies. An anaesthetic wand was dipped into FlyNap and the cotton plugs in each stock vial were gently put into. In order to avoid any flies from drowning in feeding media, the stock vials were arranged horizontally on the lab bench. In order to prevent cross-contamination, all of the flies from each vial were placed on separate index cards once the wands were removed. According to their body shape, the flies were identified as either male or female using a dissecting scope. For ease of examination, a lamp light was employed.
Transferring five male and five female flies from each cross set to the culture vials was done with a paintbrush. The vials were once again positioned horizontally on the laboratory bench. A cotton plug was placed in each culture vial before it was sealed, and any remaining flies were returned to their original containers. The vials were delivered back to the TA, where they will be stored until further notice. Putting the parent flies to sleep and removing them from the vials as soon as larva could be detected in fly culture vials helped prevent cross-breeding. The flies were put to sleep and deposited onto notecards after it became clear that numerous F1 progeny had grown into adults. Flies were examined under dissecting microscopes, with each fly's eye colour and wing presence being documented for each individual. The sex and phenotype of each fly were recorded in cross set E. They were then thrown into the mortuary once each cross set was completed.
Cross Set: C
Table 1: F1 phenotypes for cross set C
Phenotype |
Total number |
|
Eye color |
Wing size |
|
Red |
Long |
39 |
Sepia |
Long |
9 |
The F1 data that was collected for cross set C is indicated in Table 1. The number of flies for each phenotype is shown.
Figure 1: Graphical representation of F1 data for cross set C
Figure 1 presents the data from Table 1 in the form of a bar graph. According to this data, there were more flies with wildtype red eyes (39) compared to flies with sepia eyes (9). There was a total of 48 flies for cross set C.
Cross Set: E
Table 2: F1 phenotypes and sex for cross set E
Phenotype |
Number of Male Flies |
Number of Female Flies |
Total number |
|
Eye color |
Wing size |
|||
Red |
Long |
10 |
9 |
19 |
White |
Long |
10 |
13 |
23 |
The F1 data that was collected for cross set E is indicated in Table 2. The number of flies for each phenotype and sex is shown.
Figure 2: Graphical representation of F1 data for cross set E
Figure 2 presents the data from Table 2 in the form of a bar graph. According to this data, the number of male flies with wildtype red eyes (10) was equal to the number of male flies with white eyes (10). In addition, the number of female flies with wildtype red eyes (9) was very similar to the number of female flies with white eyes (13). There was a total of 42 flies for cross set E.
Phenotype |
Observed Number (O) |
Expected Number (E) |
Deviation (O – E) |
(O – E)² |
(O – E)²/E |
Red eyes/long wings |
39 |
36 |
3 |
9 |
0.25 |
Sepia eye/long wings |
9 |
12 |
-3 |
9 |
0.75 |
Total |
48 |
48 |
X² = 1.00 |
Chi-Square Analysis:
Table 3:Chi-square analysis for cross set C
Cross Set C: χ2 =
Degrees of freedom (df) = 1
p-value range = 0.1 < p < 0.9
Table 4: Chi-square analysis for cross set E
Phenotype |
Observed Number (O) |
Expected Number (E) |
Deviation (O – E) |
(O – E)² |
(O – E)²/E |
Red eyes/long wings |
19 |
21 |
-3 |
9 |
0.429 |
White eyes/long wings |
23 |
21 |
2 |
4 |
0.190 |
Total |
42 |
42 |
X² = 0.619 |
Cross Set E: χ2 =
Degrees of freedom (df) = 1
p-value range = 0.1 < p < 0.9
Chi-square tests were performed on both crossings to compare the observed and predicted values. Cross set C's p-value ranged from 0.1 to 0.9. There was a similar range of p-values for cross sets E and F. Thus, the null hypothesis for both crossings of the chi-square test cannot be rejected.
It appears that our study idea was confirmed in each mating cross of this experiment. According to the Mendelian Law of Segregation, alleles are isolated from each other during gamete production, thus we predicted that the phenotypic ratio for a hybrid with red-eyed wild-type flies would be 3:1. As predicted, cross set C generated around three times as many red-eyed wildtype flies as cross set B. We wanted to know what the predicted phenotypic ratio would be when mating red-eyed flies with white-eyed flies in our other monohybrid cross. Due to the Mendelian Law of Segregation, we predicted that the phenotypic ratio would be 1:1. As expected, cross set E generated an equal number of red- and white-eyed flies. Mendel's rule of segregation precisely predicted the results of the cross sets C and E, as demonstrated by the data. Chi-square analysis shows that the actual numbers were extremely near to what was predicted by the model's inputs. Cross sets C and E had p-values ranging from 0.1 to 0.9. These p-values were found to be more than 0.05, hence we should not reject the null hypothesis. Observed data not being statistically different from the predicted data suggests that the null hypothesis was not rejected.
In the case of cross set C, total dominance was established to be the mechanism of inheritance. When both alleles are present, the dominant allele totally overpowers the recessive allele. Recessive sepia allele was concealed since both parents were determined to be heterozygous for eye colour (Bb). According to Mendel's rule of segregation, the ratio of red-eyed flies (BB or Bb) to sepia-eyed flies (bb) is 3:1 in cross set C's F1 data, indicating that wild type red eyes predominate over sepia eyes.
Cross set E's method of inheritance was found to be X-linked. Only men in a family are often affected by X-linked recessive genetic disorders. This is because the X chromosome contains altered or mutant genes. Females are born with two X-chromosomes, thus one functioning gene can hide the effects of a mutant gene on the other, which is equivalent to full dominance. In most cases, they won't be impacted by the disease. Because males have just one X chromosome, they will be impacted if they receive an X containing a mutant gene (XwY). Because red-eyed flies were found in same numbers as white-eyed flies on cross set E, the sex chromosome is responsible for the red-eyed and white-eyed features. This suggested that the red-eyed female flies were heterozygous for eye colour (X+Xw), because the contribution of a mutant allele from both parent flies would result in offspring with red eyes and white eyes in equal proportions..
Thomas Hunt Morgan's work with D. melanogaster yielded results that are similar to these. One of the genes that affects eye colour was found in his experiment. In the eyes, the white hue of this mutant gene was clearly visible. Morgan discovered that the gene for eye colour was inherited in distinct ways depending on the fly's sex. Female flies have two X chromosomes, but male flies only have one X chromosome and a Y chromosome. This resulted in this discrepancy. Morgan discovered that the X chromosome's inheritance pattern was identical to this gene's. Thus, Morgan came to the conclusion that this gene was X - linked.
It is a shortcoming of our experiment that we only counted progeny once. Mendel's law of segregation's anticipated ratios may have been closer to the results after several counts. Another drawback is the difficulty of quickly distinguishing male flies from female flies.
D. melanogaster has shown to be a useful and versatile tool for laboratory research in this study. Research that would not be feasible without the fruit flies has been made possible thanks to these seemingly inconsequential creatures. Using D. melanogaster in pharmacological investigations is something I intend to pursue in the future.
D. melanogaster might be a useful model for drug research since it has many physiological systems with humans. Type 2 diabetes therapy might considerably benefit from the development of a novel medicinal molecule that I am working on. I sincerely hope that the work being done with these flies will lead to more breakthroughs in a variety of scientific domains, which will ultimately benefit all of humanity.
Jennings, B. H. (2011). Drosophila – a versatile model in biology & medicine. Materials Today, 14(5), 190-195. doi:10.1016/s1369-7021(11)70113-4
Morgan, T. H. (1910). Sex Limited Inheritance In Drosophila. Science, 32(812), 120-122. doi:10.1126/science.32.812.120
Pandey, U. B., & Nichols, C. D. (2011). Human Disease Models in Drosophila melanogaster and the Role of the Fly in Therapeutic Drug Discovery. Pharmacological Reviews, 63(2), 411-436. http://doi.org/10.1124/pr.110.003293
Prüßing, K., Voigt, A., & Schulz, J. B. (2013). Drosophila melanogaster as a model organism for Alzheimer’s disease. Molecular Neurodegeneration, 8, 35. http://doi.org/10.1186/1750-1326-8-35
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