Comparison between the mutant phenotypes of Drosophila Melanogaster
Abstract
The purpose of this lab report is to outline the comparison between the mutant phenotypes of Drosophila Melanogaster, commonly known as Fruitfly to phenotypes of the Wild-type flies. In this experiment, the phenotypes are compared in the resulting F1 and F2 generations. The F1 and F2 were used in generating the two mutants that were used in setting up the parental cross; hence the appropriate phenotypic ratios were used. In the F1 generation, the white eye mutant was identified on 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
The fruit fly, commonly known as Drosophila melanogaster, is an organism that is frequently used in studying different biological processes such as inheritance and genetics. 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. 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 that includes egg, larva, pupa and adult (fly). A single female fly can lay up to 100 eggs each day for up to 20 days, and the embryo will take about ten days to mature fully into adult life.
Sex difference of Drosophila melanogaster
The various ways of differentiating male Drosophila from the female one are;
- Body size. The female one is usually larger than the male one.
Figure 1
- The shape of the abdomen: the females possess a curved belly while the male belly is usually round and shorter.
- 2
- other distinguishing features are: the mark appearing on the abdomen, the sex comb, and the sex organ at the stomach.
- hereditary genes
- to observing their mutants, one needs to familiarize with the physical appearance of the wild-type fly, which is most common in the natural habitat. Although various mutations in Drosophila are known, the relevant ones are listed here below.
- The eyes
- the eyes are red and oval.
- The eyes are white, red.
- Wings
Wild-Type: Wrinkled
Mutants: Normal wings, vestigial, no wings at all. Wings change in position and size and shape.
- Body colour:
Wild-type: Yellow, basically grey having patterns of distribution of light and dark regions.
Mutants: Varying black colour, yellow, and the tone often is identified on the legs and wing veins.
The mutants’ traits are taken as recessive to the wild-type.
Material and Apparatus
- Drosophila melanogaster
- Filter Paper
- Petri dish and a cover
- 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 the bottle closed for few seconds for the ether gas to completely diffuse into the entire bottle
The base of the container is stricken lightly on the palm to drop the flies to the bottom of the bottle
The bottle cap was then removed 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 separated from the cover.
The flies were then subjected to the ether for a short time; a minute until they stopped moving.
The etherized flies were then transferred to filter paper
They were then examined using a dissecting 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
The mutants and the wild types are identified and their morphology examined before the crosses.
In the monohybrid crosses, the male red-eyed fruit fly and the White-eyed females were mated
10 Male and ten female Drosophila are shifted into the bottle containing new medium and closed with cotton. The rest flies were killed and the traits observed.
After a few days, the fruit fly will mate, and the females lay eggs that later hatched.
The experiment is repeated with red-eyed females
F2 generation analysis
The F2 generation Drosophila are killed in the Fly nap and placed 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 law of segregation by Mendel, the inheritance 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 examined by setting up the cross of male wild type st+st+ with White female eyes stst
Number of progeny
Males
Females
Total
Wild type
13
23
36
White eyes
0
0
0
By crossing the F1 and according to the Mendelian law, the resulting F2 flies are as shown.
Number of progeny
Males
Females
Total
Wild type
27
38
65
White eyes
7
12
19
A chi-square test was performed on the F2 data to show the statistical relevance of the results, as shown below.
Class
Observed
Expected
(O-E)2
(O-E)2/E
Wild type
65
63
(64-64)2 =4
0.06
White eyes
19
21
4
0.19
Totals
84
84
0.25
From the table, the degree of freedom is given as one hence p = 0.5.
Discussion
The resulting parental crosses show that the wild type allele is the most dominant in the White-eyes as there was no White progeny witnessed in the F1 progeny.
Consequently, from the F2 data, it is clear that the ratio of the normal eye of the wild type to the White-eyed is 3:42:1. This ratio is very close to the expected proportion 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.