Drosophila melanogaster crosses

Drosophila Melanogaster Crosses
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TERM 3 BIOLOGY ASSIGNMENT
Part A
Animal testing and research has been a significant contribution to the world of science and medicine as we know it. For the last couple of years the topic of animal testing has become more controversial and has been receiving more critique from animal protection and animal rights groups (Rachel Hajar). Animal research is seen as an important scientific research tool because as a result of it, an abundance of medical discoveries were made (Dave Anderson, 2016). Such discoveries include insulin, the polio vaccine, the development of pacemakers, cardiac valve substitutes and anesthetics (AnimalResearch.info, 2015). Animal Research also has had an important influence on the understanding and treatment of many diseases including breast cancer, brain injury, childhood leukemia, cystic fibrosis, malaria, multiple sclerosis, tuberculosis etc (Elizabeth Fisher, 2013). It is also believed that without animal research modern medicine wouldn’t be as advanced, and the removal of the practise would only elongate the process of developing lifesaving treatments (Dave Anderson, 2016). Animal testing should be continued because it has a remarkable impact on improving the changing world of medicine. Some arguments against animal testing include that it’s an unethical practices, but legislations such as the Animal Care and Protection Act in Queensland and others around australia were created to combat and prevent any inhumane treatment towards animals during research (AnimalResearch.

info, 2016)(RSPCA, 2018). Other arguments include that alternative testing methods are available, and that animal biology is different to human biology therefore animals make terrible test subject. Even though it may be complex, human biology shares many similarities with animal biology, specifically with mammals because they share common ancestry (Kara Rodgers, 2007). The use of alternative methods such as cell culture testing or computer models, instead of animal testing is unrealistic because those methods wouldn’t identify potential side effects affecting other organs in the body and/or they would make it difficult to identify whether a product is effective on a living organism (Kara Rodgers, 2007). Many mistakes made in the past with untested drugs prove that animal testing is crucial and it prevents many consequences. Examples include the 1937 ‘Elixir Sulfanilamide’ incident, were a pharmaceutical company released an untested drug that contained diethylene glycol (DEG) which poisoned and killed hundreds of casualties (Rachel Hajar, 2011). And during the 1950s and 60s when the thalidomide drug was also untested and was claimed effective as a painkiller and was found to help with the effects of morning sickness, but had the devastating effect of causing birth malformations in ten thousand children across forty-three countries (Rachel Hajar, 2011). Such cases highlight the significance of animal testing in the modern world, they prove that without being tested, products could cause mass harm to the general public. Animal testing and research has significantly assisted in the development of modern science and medicine, and it will continue to be a crucial part for discovering new cures for current and emerging diseases.
Abstract
The aim of the experiment was to identify whether results from theoretical dihybrid crosses accurately predict the results from actual cross. This was accomplished by conducting two sets of F1 crosses, one with white-eyed normal winged male Drosophila crossed with red-eyed vestigial winged female Drosophila, and the other with red-eyed vestigial winged male Drosophila crossed with white-eyed normal winged female Drosophila. Some of the F1 offspring were then crossed again to produce the F2 generation. These were then counted to achieve the final results.
Introduction
Drosophila Melanogaster, commonly known as fruit flies, are labeled as the most significant organisms in biological research. Their use dates back to 1901 by William Castle’s group in Harvard. In 1933 a Nobel Prize in Physiology or Medicine was won by Thomas Hunt Morgan for “his discoveries concerning the role played by the chromosome in heredity” (Barbara H.Jennings, 2011). He used Drosophila to identify genes and he recognised that they were located with chromosomes before it was known that DNA is genetic material (Barbara H.Jennings, 2011). And again in 1946 Herman Muller won a Nobel Prize for discovering the harmful effect of x-rays on chromosomes through the use of Drosophila ( Barbara H.Jennings, 2011). The use of Drosophila in labs has continued to increase because the flies are easy to grow, maintain, and study. They also have a variety of orthologous genes linked to human disease (Karen G Hales, 2015). Because of such reasons, the Drosophila is a model organism and is the best organism for use in this experiment. The first factor that makes the Drosophila the best choice is that they are easy to grow. The lifespan of the Drosophila is approximately two weeks, this is significant because it allows for more frequent reproduction which also grants quick production of large numbers of generations of offsprings (Karen G Hales, 2015). Second advantage of the drosophila flies are that they are easy to keep, because the food required to keep the insects alive usually only consist of cornmeal/yeast/agar base mixed with various carbohydrates and preservatives (Karen G Hales, 2015). Another advantage is that the drosophila is easy to study, this is because the flies only have four chromosomes, four autosomal and two sex chromosomes (modENCODE, 2018). The manageable number of chromosomes makes it relatively easy to study the genetic makeup of the flies. The mutant phenotypes, of having white eyes or vestigial wings, is very identifiable in Drosophila, which makes them efficient in crossing experiments and inheritance patterns (Christin E. Arnini, 2018). During his studies Thomas Morgan recognised that since wild-type flies have red eyes, the white eyes characteristic is a mutant phenotype (T.H. Morgan, 1910). He completed an experiment where he crossed red-eye females with male white-eyed flies. He then crossed the F1 generation produced to get his final results. His results consisted of only having three white-eyed male flies out of the 1237 produced in the first cross, and only 782 white-eyed males out of 1011 male offsprings and 2459 red-eyed females offsprings (T.H. Morgan,1910). Morgan considered the results produced and distinguished that the white-eye phenotype is a sex-linked trait. Vestigial Wings in the Drosophila is when the wings are mutated and become shortened leaving the flies crippled (E. David Peebles, Sharon K. Whitmarsh, and Matthew R. Burnham, 2001). This is a recessive trait controlled by an autosomal gene, and the flies with normal wings would have at least one dominant gene (e.g. ethier VV OR Vv) for normal wings while, while the affected flies will only have recessive genes (e.g. vv) resulting in vertiglide wings (E. David Peebles, Sharon K. Whitmarsh, and Matthew R.Burnham, 2001).
Aim
The aim of this experiment is to identify whether results from theoretical dihybrid crosses accurately predict the results from actual crosses using live Drosophila melanogaster.

Materials
Two homozygous cultures of Drosophila melanogaster
(Normal wings/white eyes, Vestigial wings/red eyes)
empty culture bottles (large and small)
commercial powdered food supply
white tissues
ice brick
small paint brush
stereomicroscope and/or magnifying glass
incubator set at 23OC
freezer
Method
Food was prepared in two small culture bottles as per the instructions on the packet.
Flies were collected and anaesthetised (using the chilling method) and were identified as male or female.
An F1 cross was set up using a small number of males with normal wings/white eyes and a small number of virgin females with vestigial wings/red eyes.
Another F1 cross was set up using a small number of males with vestigial wings/red eyes and a small number of virgin females with normal wings/white eyes.
These crosses were incubated for 7 days before all adults were removed.
After the F1 offspring had emerged, food was prepared in large culture tubes and approximately 5-8 flies of both sexes were moved into the fresh tubes to produce the F2 generation.
These crosses were incubated for 7 days before all adults were removed.
Once approximately 100 F2 offspring were produced, the final count was performed.
Hypothesised Results
First cross- White-eyed, normal winged males and vestigial winged, red-eyed females cross:
let V= normal wings and v= vestigial wings
Let R= red eyes and r= white eyes
Male Genotype: XVr YFemale Genotype: Xv R Xv R or X v R Xr vXv RXv RX v RXv rXVrXVrXv RXVrXv RXVrXv RXVrXv rYXv RYXv RYXv RYXv rYFemale: 4 out of 8 or 50%
Normal winged, red-eyed: 3 out of 4 or 75%
Normal winged, white-eyed: 1 out of 4 or 25%
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 0
Male: 4 out of 8 or 50%
Normal winged, red-eyed: 0
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 3 out of 4 or 75%
Vestigial winged, white-eyed: 1 out of 4 or 25%
It is predicted that 100% percent of the female offspring produced from the first cross will have normal wings, and of those 75% will most likely have red eyes and 25% white eyes.
It is also predicted that from the same cross 100% of the male offspring are most likely to be vetsigled winged and of those, 75% most likely to be red-eyed and 25% white eyed.
Second cross-White-eyed, normal winged females and vestigial winged, red-eyed male cross:
let V= normal wings and v= vestigial wings
Let R= red eyes and r= white eyes
Male Genotype: Xv R YFemale Genotype: XV r XV r or X V r Xr vXV rXV rXV rXv rXv R XVrXv RXVrXv RXVrXv RXv rXv RYXV rYXV rYXV rYXv rYFemale: 4 out of 8 or 50%
Normal winged, red-eyed: 3 out of 4 or 75%
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 1 out of 4 or 25%
Vestigial winged, white-eyed: 0
Male: 4 out of 8 or 50%
Normal winged, red-eyed: 0
Normal winged, white-eyed: 3 out of 4 or 75%
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 1 out of 4 or 25%
It is predicted that 100% percent of the female offspring produced from the second cross will have red eyes, and of those 75% will most likely have normal wings and 25% vestigial wings.
It is also predicted that from the same cross 100% of the male offspring are most likely to be white eyes and of those, 75% most likely to be normal winged and 25% vestigial winged.
RESULTS
F1 First Cross:
White eyed, normal winged males X Vestigial winged, red eyed females.
Characteristics Number of males Number of females
Red eyed with normal wings 11 9
White eyed with normal wings
Red eyed with vestigial wings
White eyed with vestigial wings 3
The above table shows the first F1 cross between white-eyed normal winged male Drosophila and vestigial winged red-eyed female Drosophila.
Male: 14 out of 23
Normal winged, red-eyed: 11 out of 14 or about 79%
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 3 out of 14 or about 21%
Female: 9 out of 23
Normal winged, red-eyed: 9 or 100%
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 0
F1 Second Cross:
Vestigial winged, red eyed males X White eyed, normal winged females.
Characteristics Number of males Number of females
Red eyed with normal wings 10
White eyed with normal wings 10
Red eyed with vestigial wings
White eyed with vestigial wings
The above table shows the second F1 cross between red-eyed vestigial winged male Drosophila and normal winged white-eyed female Drosophila.
Male: 10 out of 20
Normal winged, red-eyed: 0
Normal winged, white-eyed: 10 or 100%
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 0
Female: 10 out of 20
Normal winged, red-eyed: 10
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 0
Vestigial winged, white-eyed: 0
F2 First Cross:
White eyed, normal winged males X Vestigial winged, red eyed females.
Characteristics Number of males Number of females
Red eyed with normal wings 9 24
White eyed with normal wings 9 0
Red eyed with vestigial wings 2 12
White eyed with vestigial wings 4 0
The above table shows the first F2 cross between white-eyed normal winged male Drosophila and vestigial winged red-eyed female Drosophila.
Male: 24 out of 60
Normal winged, red-eyed: 9 out of 24 or about 37.5%
Normal winged, white-eyed: 9 out of 24 or about 37.5%
Vestigial winged, red-eyed: 2 out of 24 or about 8%
Vestigial winged, white-eyed: 4 out of 24 or about 17%
Female: 36 out of 60
Normal winged, red-eyed: 24 out of 36 or about 67%
Normal winged, white-eyed: 0
Vestigial winged, red-eyed: 12 out of 36 or about 33%
Vestigial winged, white-eyed: 0
F2 second cross:
Vestigial winged, red eyed males X White eyed, normal winged females.
Characteristics Number of males Number of females
Red eyed with normal wings 20 24
White eyed with normal wings 16 21
Red eyed with vestigial wings 3 5
White eyed with vestigial wings 8 3
The above table shows the second F2 cross between red-eyed vestigial winged male Drosophila and normal winged white- eyed female Drosophila.
Male: 47 out of 100
Normal winged, red-eyed: 20 out of 47 or about 43%
Normal winged, white-eyed: 16 out of 47 or about 34%
Vestigial winged, red-eyed: 3 out of 47 or about 6%
Vestigial winged, white-eyed: 8 out of 47 or about 17%
Female: 53 out of 100
Normal winged, red-eyed: 24 out of 53 or 45%
Normal winged, white-eyed: 21 out of 53 or 40%
Vestigial winged, red-eyed: 5 out of 53 or about 9%
Vestigial winged, white-eyed: 3 out of 53 or 6%
Discussion – write it please
As it is seen above, before the first cross, it was expected that between the female flies to be produced, 75% would have normal wings and red eyes while only 25% were expected to have normal wings and white eyes. What is more, all females were expected to have normal wings. Concerning the male subjects, they were all expected to have abnormal wings. 75% of them were anticipated to have red eyes and 25% white eyes. That was the hypothesis. However, the results showed differences to the initial hypothesis. 100% of the females had normal wings and red eyes. 79% of the male population had normal wings and red eyes while 21% of them had abnormal wings and white eyes. Consequently, during the first cross, the characteristic of white eyes was only seen in males. In addition, males which had white eyes also had abnormal wings. It should be noted that while all males were anticipated to have abnormal wings, this was not the case, as only 21% of them had abnormal wings. That is an important observation that should be taken into consideration. After the repetition of the first cross occurred, it was observed that 75% of males had normal wings, of which half of them had red eyes and the rest had white eyes. The remaining 25% of males had abnormal wings, of which 8% had red eyes and 17% had white eyes. As for the females, 67% of them had normal wings and 33% had vestigial wings. All females were red-eyed.
As far as the second cross is concerned, the hypothesis was that 75% of the female population would be born with normal wings, while 25% of it would have vestigial wings. All female flies were predicted to be red-eyed. On the other hand, 75% of the male flies were predicted to have normal wings while the remaining 25% would be born with vestigial wings. All males were anticipated to be born with the recessive trait of white eyes. The results showed that 100% of the male population was normal winged and had white eyes. Also, 100% of the female population had normal wings and red eyes. After the repetition of the cross, 77% of the produced males were normal-winged and 23% had abnormal wings. Concerning their eyes, 51% had white eyes while 49% had red eyes. It should be kept in mind that only 6% of males had abnormal wings accompanied with the characteristic of red eyes, while the combination of vestigial wings and white eyes rises to the percentage of 17%. As for the females, the vast majority of them were born with normal wings, 85% to be precise. Only a low percentage of about 9-10% had both abnormal wings and red eyes. Moreover, 45% of them had normal wings and red eyes while 40% of them had normal wings but were white-eyed.
Taken all the above into consideration, it is obvious that the genetics of the Drosophila melanogaster do not follow the rules of the Mendelian inheritance. That is because the white eyes characteristic is a mutation which is linked to the sex of the fly and the gene for it is located in the sex chromosome. Since the results showed that female flies with white eyes were produced, that rules out the possibility that the recessive trait of white eyes is only located in the Y chromosome and thus found only in males. As most inherited genes are found in X chromosomes, one could assume that this mutation is located in the X chromosome and is activated in some special occasions.
Conclusion
Bibliography
References
Anderson, D. (2015). Top 10 Reasons Why Animal Testing is Necessary. [online] ListLand.com. Available at: https://www.listland.com/top-10-reasons-why-animal-testing-is-necessary/ [Accessed 21 Aug. 2018].
Animal-testing.procon.org. (n.d.). Animal Testing – ProCon.org. [online] Available at: https://animal-testing.procon.org/ [Accessed 21 Aug. 2018].
Arnini, C. (n.d.). 96.05.01: Using Drosophila to Teach Genetics. [online] Teachersinstitute.yale.edu. Available at: http://teachersinstitute.yale.edu/curriculum/units/1996/5/96.05.01.x.html [Accessed 27 Jul. 2018].
Jennings, B. (2011). Drosophila – a versatile model in biology & medicine. Materials Today, [online] 14(5), pp.190-195. Available at: https://www.sciencedirect.com/science/article/pii/S1369702111701134#bib4 [Accessed 21 Aug. 2018].
MORGAN, T. (1910). SEX LIMITED INHERITANCE IN DROSOPHILA. Science, [online] 32(812), pp.120-122. Available at: https://www.aaas.org/.
New Internationalist. (2011). Is animal testing necessary to advance medical research?. [online] Available at: https://newint.org/sections/argument/2011/06/01/animal-testing-medical-research-laurie-pycroft-pro-test [Accessed 21 Aug. 2018].
Peebles, E., Whitmarsh, S. and Burnham, M. (2001). Basic Concepts in Drosophila melanogaster Genetics.. [ebook] MSU Department of Agricultural Communications, p.2. Available at: https://www.poultry.msstate.edu/pdf/courses/po3103/fly3.pdf [Accessed 29 Jul. 2018].
Rogers, K. (2007). Scientific Alternatives to Animal Testing – Advocacy for Animals. [online] Advocacy.britannica.com. Available at: http://advocacy.britannica.com/blog/advocacy/2007/09/scientific-alternatives-to-animal-testing-a-progress-report/ [Accessed 21 Aug. 2018].
Understanding Animal Research. (2014). Forty reasons why we need animals in research | Understanding Animal Research | Understanding Animal Research. [online] Available at: http://www.understandinganimalresearch.org.uk/contact-us/science-action-network/forty-reasons-why-we-need-animals-in-research/ [Accessed 21 Aug. 2018].