The purpose of this lab is to understand concepts that are related to genetic crosses. For this specific lab, Drosophila melanogaster were used. Drosophila melanogaster is also known as fruit flies. Created by Gregor Mendel, this experiment uses genetic rules. The purpose for the use of genetic rules is to determine the F1 generation. “Drosophila melanogaster has been widely used in the biological sciences as a model organism. Drosophila has a relatively short life span of 60-80 days, which makes it attractive for life span studies.” (Staats, 2018) Each group was given fly nap to knock out their own flies and observe them in a span of two weeks. During the two weeks, the F1 created a new generation which the allowed the students to observe and record the mutation. The hypothesis was that the F2 generation will follow the 9:3:3:1 ratio.
It has been a discovery that the fruit fly is a convenient organism for carrying out experiments in genetics. (Silverman, 1954) Drosophila do not require sophisticated equipment and are rather cheap, there are fewer ethical issues involved in experimenting Drosophila compared with studies in laboratory rodents, such as rats or mice. Drosophila is often fed complex solid diets such as yeast, corn, and agar. (Staats, 2018) The formation of mendelian genetics occurred during the first decades of the twentieth century by Gregor Mendel. Mendelian genetics are the basic principle of heredity. A dihybrid cross is a cross between two different genes that possess two overserved traits. An allele is one of the possible forms of a gene, most genes have two alleles which would be dominant or recessive. A dominant is opposed while recessive is expressed when two copies of the gene are present. The expected ratio in the offspring from a heterozygous cross is 9:3:3:1 A gene is comprised of nucleotides. It is responsible for the physical and heritable phenotype of an organism. The different types of mutations that are seen in Drosophila are Apterous, Vestigial, Sepia, and Ebony. Apterous mutant was first found by Miss Edith M. Wallace in 1913 while working in the laboratory of Dr. T. H. Morgan. This mutant was shown to be recessive and located on the second chromosome. (Butterworth, 1965) When the flies have wings that are shriveled up, it is known as Apterous. Vestigial gene of Drosophila encodes a nuclear protein which plays a key role in wing formation but is also involved in other developmental processes, it is between the Apterous and the wild type. (Zider, 1966) Flies are usually red, but when they are black it is known as Sepia. When the body of the fly is black, it is known as Ebony. The purpose of this experiment was to see the results when unknown F1 generation crosses with the wild type phenotypes. For the null hypothesis, experimenters used the chi-square to conclude that the class data was closely associated with the phenotypic 9:3:3:1 ratio. The chi-square is used to determine whether there is a significant difference between the expected frequencies. Studying genetics is important because you can see how heritable traits are transmitted from parents to offspring. (Mary, 2013)
Materials and Methods
For the experiment, students had performed two genetic crosses with Drosophila. Before observing the flies, the students set up two cultural tubes, one for each cross. To start off, add one spoon of dry media to the vial to about 1/5 to 2/5 volume. Next, the students added water until media appears completely moistened. Then add 2-3 grams of yeast to the tubes. Adding addition water if needed, allow the vial to sit for a few minutes. The students took one of the prepared vials and labeled it with sex-linked cross, their group names, date, and section of the lab. After the flies were given to the students, the students used a brush and microscope to separate them by male and female. Students placed 2 males and 3 females in the vial and secured it tightly with a cotton ball. Moving onto the second prepared vial, the students also labeled it with their group name, date, and section. Obtaining more sleeping flies from instructor, students placed the flies under the microscope paying specific attention to eye color, wing shape, and body color. Next, they placed 2 males and 3 females on the side of the vial and kept it on its side until the flies woke up. The vial was then tightly secured with one or two cotton balls. The students used excel to calculate the chi-square analysis. They also used the p-value chart to determine the data significance. To accept the null hypothesis, the p-value had to be higher than .5 and to reject the null hypothesis, the p-value had to be smaller than .
The objective of this lab was to determine the difference between observed and expected values. The data that is represented in figure 1 is a Punnett square for the unknown cross, it shows a dihybrid cross with the ratio of 9:3:3:1. The square is suggesting that 9/16 flies will have normal genes while 3/16 will have normal wings and/or abnormal eyes. 1/16 flies will have both abnormal wings and eyes. Figure 2 shows the difference between the class data and the expected value in which the total can out to be 6.0778055078. Figure 3 shows p-value vs chi-square which helps determine if the hypothesis is accepted or rejected. The hypothesis in this case is accepted because it is higher than 0.5. One alternative could be that some of the flies dying due to not getting enough food. Another alternative could be that some of the flies died due to getting stuck in their food and not being able to make it out of it or the flies may have not been able to reproduce efficiently. This experiment could be further improved by giving each group more than 1 sample of flies. In other words, if the first sample of flies did not work out, then the group had the second sample to turn to. The controls in this lab were the number of flies that were distributed to each group. Another control would be how much food was put into the tube.
To enhance this study in the future, an idea would be to have 2 sample of flies or to carefully place the flies in the tube so that they don’t get stuck in their food. Drosophila can be used in molecule discovery by taking the advantage of genetics that are available. (Pandey and Nichols, 2011) Some important features such as “oral availability, metabolic stability and low toxicity” are found by preforming drug screening of the Drosophila melanogaster. (Pandey and Nichols, 2011) The research is very much significant. It can be led to many other discoveries.
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- Marian J. Silverman. “The Effect of the Two Factor Cross Involving Vestigial and Miniature Wings upon Wing Shape of Drosophila.” Bios, vol. 25, no. 2, 1954, pp. 91–106. JSTOR
- Pandey, U. B., and C. D. Nichols. “Human Disease Models in Drosophila Melanogaster and the Role of the Fly in Therapeutic Drug Discovery.” Pharmacological Reviews, vol. 63, no. 2, 2011, pp. 411–436., doi:10.1124/pr.110.003293.
- Staats, Stefanie, et al. “Drosophila Melanogaster as a Versatile Model Organism in Food and Nutrition Research.” Journal of Agricultural and Food Chemistry, vol. 66, no. 15, 2018, pp. 3737–3753., doi:10.1021/acs.jafc.7b05900.
- Zider, A., et al. “Vestigial Gene Expression In Drosophila Melanogaster Is Modulated by the DTMP Pool.” MGG Molecular & General Genetics, vol. 251, no. 1, 1996, pp. 91–98., doi:10.1007/bf02174349.