SC BIOL 101 - Drosophila Melanogaster (12 pages)

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Drosophila Melanogaster



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Drosophila Melanogaster

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Pages:
12
School:
University Of South Carolina-Columbia
Course:
Biol 101 - Biological Principles I
Biological Principles I Documents
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BIO 101L EXPERIMENT 9 DROSOPHILA MELANOGASTER MENDELIAN GENETICS FOR AN UNKNOWN DIHYBRID CROSS USING AN F2 GENERATION TO DETERMINE P1 GENERATION Report Author Cameron G Kahn Report Submitted 12 November 2014 Data Collected 29 October 2014 Laboratory Partners Nilesh Syam Taylor Hollingsworth Teaching Assistant Amanda Havighorst Author s Affiliation Department of Chemistry and Biochemistry University of South Carolina Columbia SC 29208 I pledge that my work meets the standard of the USC Honor Code ABSTRACT This experiment was performed to study phenotypes of the Drosophila melanogaster which is simply a red eyed fruit fly By studying phenotypes of the fly a better understanding of genetics can be accomplished In the case of this experiment the phenotypes being studied were the wild type eyes red sepia brown eyes wildtype wings and the shriveled wings both Vestigial and Apterous in the F 2 generation Using the offspring observed from the F1 parent generation the parental P1 generation flies mated at the supply company was determined to be homozygous dominant and homozygous recessive The observed number of flies for each phenotype was compared with the expected number for each phenotype using Mendel s Law to see if 1 the results followed Mendelian Genetics The null hypothesis was that the results from the class data collected for the observed number of flies for each phenotype would follow Mendelian Genetics A chi squared statistical test was performed and the results showed that the observed data did not follow the 9 3 3 1 ratio as described by Mendelian Genetics therefore the null hypothesis was rejected because the data observed was significantly different at the 95 confidence interval than what was expected using Mendel s Law which concludes that the results from the experiment could have been due to random error INTRODUCTION The drosophila melanogaster is a species of fly that is heavily studied in biology to understand the basics of genetics development and cellular processes The fly is a common vinegar fruit fly that is likely to be seen around bananas at the supermarket The drosophila fly acts as a model species for understanding more complex species such as higher eukaryotes all the way up to humans through the study of its genome and its ability to culture quickly in lab 1 In the early twentieth century a scientist by the name of Thomas Hunt Morgan first observed white eye mutation in drosophila and began experimenting with crossing with wild type drosophila He later performed crossing the mutant drosophila and therefore concluded that the red eye offspring from the first cross with the white eye male and the wild type female was dominant over the recessive white eyes 2 After further study Morgan realized that these phenotypical traits were sex linked and relied on the X chromosome due to his observation that all the females had red eyes while the males had both red and white eyes From here crossing the drosophila flies to expose other desired phenotypes began One of 2 Morgan s most important conclusions is that the number of red eye versus white eye drosophila follows Mendelian Genetics and the number of flies that display either phenotype can be predicted using Mendel s ratio of 3 1 2 Gregor Mendel was an Augustinian monk who created the basic laws regulating the traits passed on from one generation to the next parent to offspring Mendel s experimentation with pea plant s seed color pea color and the crossing of the peas between the years of 1856 to 1863 founded the understanding of heredity and from this came the formation of the laws of Mendelian inheritance 3 Around 1866 Mendel discovered the invisible elements known today as genes The laws of inheritance created by Mendel serves to describe how alleles are represented in gametes and offspring 2 The background provided by Mendel s research back in the 1800s is still the foundation for modern genetics today The focus of this experiment was on the unknown dihybrid cross of the offspring from the parent generation The experiment was performed with the understanding of Mendel s first and second laws of inheritance Mendel s first law is called the law of segregation and can be defined as when the parental alleles segregate during gamete formation therefore creating gametes that only contain one allele for every gene 2 Mendel s second law is known as the law of independent assortment and it stated that allelic pairs separate self reliantly of other pairs From the second law Mendel concluded through observation that there is a 9 3 3 1 ratio of all the possible combinations of phenotypes traits With the knowledge provided from the first and second laws of inheritance the ratio of phenotypes and genotypes for offspring can be predicted 4 Furthermore one can work backwards based on the outcome of either a 3 monohybrid cross or in this case a dihybrid cross to determine the genetic make up of the parent generation For this experiment this was done using a Punnett square in order to map out the outcomes from the cross In this experiment the purpose was to apply Mendel s laws in order to study inheritable traits of the drosophila melanogaster from an unknown dihybrid cross and then determine the parent generation From the knowledge of Mendelian Genetics the null hypothesis was that the four phenotypes displayed in the dihybrid cross would follow the 9 3 3 1 ratio predicted using Mendel s second law of inheritance METHODS This lab was performed over two weeks time The first portion of the lab was to set up two culture tubes one for each cross however only the unknown dihybrid cross vial was significant in observing for this experiment A spoon full of dry high carbohydrate media was obtained and placed into the first culture vial The vial was then filled with about 10mL of water until the media was slightly moistened The vial was let standing for a brief minute or so and water was added until the surface displayed a shiny appearance One to two yeast grains were then added to the vial so that not too much carbon dioxide builds up which slows development of any offspring The vial was closed using cotton balls and then let sit for about 5 minutes to ensure the media solidified If the media was not solidified after the 5 minutes by tipping the vial on its side and checking for any media to pour down the side of the vial the media would need to be remade and the procedure would need to restart with a new vial Having the media solidified


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