Genetics in Drosophila melanogaster

Genetics in Drosophila melanogaster

Abstract

This report aims at outlining the comparison between the mutant phenotypes of Drosophila Melanogaster, commonly known as Fruit-fly to phenotypes of Wild-type flies. In the experiment, the phenotypes are compared in the resulting F1 generation and the F2. The F1 and F2 were used in generating the two mutants that were employed in setting up the initial crossing of the parents; hence the appropriate phenotypic ratios were used. From F1, the white eye mutant was identified for the male fruit fly. In the subsequent F2 generation, there was newly identified mutant in both male and female in which two distinct phenotypes, the white eye mutant were observed again. Prediction of this outcome had much to do with the result which was created by setting up white-eyed males and wild type females

Introduction

Drosophila melanogaster is an organism that is frequently used in studying different biological processes such as inheritance and genetics (Sharma, et al. pg.5). The use of this organism has various advantages in that it is easy to maintain and handle, cheap to culture in laboratories, they possess short life cycle as compared to other bodies, and they produce a large number of embryos that are laid externally (Sharma, et al. pg.7). Their shorter life implies that it would take a few weeks to complete an experiment that would otherwise take several months and years in other vertebrate organisms to complete.

Drosophila melanogaster undergoes a life cycle of four stages; egg, larva, pupa and adult. A female fly can lay 100 eggs each day for 20 days, and the embryo will take about ten days to mature fully into adult life (Sharma, et al. pg.15).

Sex difference of Drosophila melanogaster

The various ways of differentiating male Drosophila from the female one are;

• Size of the body: The female one is usually larger compared to the male one.

Figure 1. Body size comparison (www.exploratorium.edu)

• The shape of the abdomen: the females possess a curved belly while the male belly is usually round and shorter.

Figure 2. The shape of the abdomen (www.exploratorium.edu)

Other distinguishing features are: the mark appearing on the abdomen, the sex comb, and the sex organ at the abdomen.

Hereditary gene

Before observing the mutants, it is prudent to familiarize with the physical outlook of the wild-type fly, which is commonly available. Although various mutations in Drosophila are known, the relevant ones are:

1. The eyes;

Wild-type: the eyes are red and oval.

Mutants: The eyes are white, red.

2. The Wings;

The Wild-Type: Wrinkled

Mutants: Vestigial, no wings at all and normal.

3. Colour of the body:

The wild-type: Yellow, grey with patterns of distribution of dark and light regions.

Mutants: Varying black colour, yellow, and the tone often is identified on the legs and wing veins.

Methodology and materials

Equipment

• Drosophila melanogaster.
• A filter Paper.
• Petri dish.
• A label
• “Commeal” medium
• Fly-nap/ether
• Vial tube and a sponge cover

Procedure

• The anaesthetizing process
• The Fly nap is dripped into the cotton wool sponge and bottle closed for some seconds for the gas to diffuse into the bottle completely
• The container base is stricken lightly with a hand to drop flies to the bottom.
• The cap of the bottle was then taken off and quickly replaced with etherized. The bottle was then inverted over the etherized and shaken till the flies enter the etherized. The container should not be altered over the etherized since the ether is more substantial than the air.
• The bottle was quickly isolated from the cover.
• The etherized flies were then transferred to filter paper
• They were then observed using a microscope
• A soft brush was used in removing flies and change their position about the stage of the microscope.
• The Drosophila was discarded after the experiment.

General procedures of the experiment

1. The mutants and the wild types are identified and their morphology examined before the crosses.
2. In the monohybrid crosses, the male red-eyed fruit fly and the White-eyed females were mated

• 10 Male and ten female flies were shifted to the bottle containing new substrate and closed with cotton. Other flies were killed and the traits observed.

1. After some days, the fruit fly mated, and the females laid eggs that later hatched.
2. The experiment is repeated with red-eyed females

F2 generation analysis

F2 generation flies are killed in the Fly nap and then displayed on the filter paper. The F2 generation phenotypes were enumerated. Based on the monohybrid crosses, there were recorded only two phenotypes.

Results

Figures 3 and 4 below shows the White and red-eyed fruit fly, respectively.

Figure 3

Figure 4.

In testing the concept of segregation by Mendel, the genetic acquisition of eye colour by crossing two breeding traits of Drosophila that are pure was examined for the wild type and the White-eyes. The below phenotype results when the dominant allele was observed by setting up the cross of the male fly of wild-type st+st+ with white female eyes stst.

By crossing F1 and according to the Mendelian law, the F2 flies are as shown.

A chi-square test on the F2 data shows the statistical relevance of the results, as shown below.

From the table, the degree of freedom is given as one hence p = 0.5.

Discussion

The resulting parental crosses show that the alleles of wild type flies were dominant in the White-eyed as there was no record of white progeny in the F1.

Consequently, from F2, it is clear that the proportion of the normal eye of the wild type to the white-eyed was 3:41:1, which is close to the expected value of 3:1 of the monohybrid cross. However, a chi-square test was also performed to confirm this data, from which the experimental data could be observed as not significantly drifting from the expected ratio of 3:1.

Conclusion

From the experiment, it can be concluded that the phenotype of the F1 generation progeny shows that the wild-type allele of White-eyed was dominant to the alleles for the red eyes.

Work Cited

Sharma, Vartika, et al. “Mighty Fly: An Introduction to Drosophila.” Insights into HumanNeurodegeneration: Lessons Learnt from Drosophila. Springer, Singapore, 2019. 1-36.

Pavin, Austin, et al. “Aversive and Appetitive Learning in Drosophila Larvae: A Simple and Powerful Suite of Laboratory Modules for Classroom or Open-ended Research Projects.” Journal of Undergraduate Neuroscience Education 16.2 (2018): A177.