Drosophila Melanogaster has been extensively studied for genetic investigations due to its ideal characteristics for the study of animal development. This species contains characteristics such as small size, approximately 1mg, which allows testers to study many at one time. In addition to being small, they can survive in small spaces, which means numerous tests can be conducted and many different mutant stocks can be maintained. Many tests are conducted in small tubes, as fruit flies do not need much space for living. Moreover, the Drosophila Melanogaster has a very simple food plan, meaning it is not hard to take care of these species during testing. They also have a short life cycle of 12 days, which allows scientists to study the life cycle of a fruit fly, and perform test crosses, very easily. Room temperature is an important factor that allows their life cycle to be completed within the 12 days. A fruit fly undergoes metamorphosis, which means it has three stages of development before reaching adulthood. The three stages consist of: egg, larval, and pupal. Egg: Fruit flies are capable of laying up to 500 eggs during their lifetime. Most eggs are laid in fruit or other decaying material. The optimal temperature for laying an egg is 75-80 degrees Fahrenheit, also known as room temperature. Larva: Larva are the small worm-like stages of a fruit fly. Larvae feed on the decaying material in which they were hatched, and tend to consume a lot of food in order to prepare for their next stage, the pupal stage. Larvae shed their skin in order to increase their size. Pupal: Pupating is a resting stage for the larvae to increase in size and begin to form into the adult fly. Fruit fly pupae are small and unnoticed. This is the last stage before the fly reaches the adult stage. Above is an image representing the life cycle of a fruit fly, starting as an egg on day 1, and ending as an adult on day 10 or sometimes 12. The fruit fly spends the longest time as a larva, growing and increasing its size to prepare for adulthood. Background Studies of the Fruit Fly: Thomas Hunt Morgan was one of the well known biologists who had studied the Drosophila in the early 1900’s. He was the first scientist to study genetic recombination and performed thousands of tests on the Drosophila. After test crossing many species of the fruit fly, his results confirmed the chromosomal theory of inheritance, which states that genes are located on chromosomes like beads on a string, and that some genes are linked. Illustrated above is Morgan’s experiment of the cross between the white eyed male fruit fly, and the red eyed female fruit fly. As the f1 generation is crossed, you can see that sex linked inheritance affects the f2 generation as one male becomes white eyed. This image is a better representation of Morgan’s conclusion.Hypothesis:If the students perform 3 test crosses between the different types of fruit flies, then the predicted ratios for the monohybrid F2 generations will be 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive because when only crossing one trait, the dominant trait typically masks the recessive trait. If the test cross is a dihybrid cross, the predicted ratio for the F2 generation would be 9:3:3:1 because the most dominant trait is presented in the F2 generation the most. The 9 to 3 to 3 to 1 ratio is supported by the law of independent assortment, which states that alleles separate independently during the formation of gametes. Make Connections: The Drosophila Melanogaster lab relates to the world today as it deals with genetics and heredity from parent to offspring. Today, genes play an important role in determining many traits that children can inherit from their family. For instance, parents can pass on their traits, such as: eye color, hair color, height, to their children or even grandchildren. The study of the fruit fly can help aid scientists in studying other organisms, such as humans. Fruit flies actually share 75% of the genes that cause disease with humans (University of North Carolina).  Therefore, studying fruit fly genetics can help study the behavior of genes and disease causing genes in humans. Also, since fruit flies are very low maintenance, many tests can be done in a very short amount of time, which speeds the research process for discovering what causes these diseases in humans. In addition, studying the fruit fly genes can help scientists find cures for the diseases that are also commonly found in humans. All in all, the study of the fruit fly is important to today’s society and scientists studying human diseases. Procedure: The students first obtained a vial containing only wild type flies, that were immobilized by chilling or FlyNap, in order to become comfortable in recognizing the difference between male and female. The males contain a darker, more blunt abdomen, and are typically smaller than females. The students then were to note specific characteristics of the wild type fruit fly, and note those characteristics down for future reference. To immobilize the flies, the students transferred all the flies from the new vial, to the old vial containing FlyNap. From there, they took a wand, or Q-tip, and dipped it into the FlyNap solution, and then transferred that into the vial. The flies were left in the vial containing fly nap for no longer than 5 minutes. Then, they were transferred onto a plate, where they were examined under a microscope. The students then were handed experimental flies, which had different characteristics than the wild type. They examined the flies and noted the varying characteristics. The students then were given three vials labeled A, B, and C. They were told to examine the flies in each vial, and determined the crosses between the males and females. Over the course of several weeks, the flies were examined, and each generation of the Drosophila were noted. In the F1 generation, certain mutations, and traits in the female and male genders were also observed carefully. The same observations were recorded for the F2 generations of each vial. After each generation was examined, the flies were placed in the morgue, and were later gotten rid of. In the graph, the results illustrate similar results for both eye colors in each sex. However, there is much more male red eyed flies than male white eyed flies. This is because red eye color is dominant over white eye color, and when a female and male produce their offspring, the males receive only one X chromosome, and receive either the dominant or recessive trait. In this case, most females must have showed homozygous dominance if many of the males received the dominant trait, being red eyes. The Drosophila Melanogaster experiment illustrates great value to the understanding of genetics and probability. Overall, the results illustrate dominant versus recessive traits. In addition, each cross contributed to understanding a different type of genetic cross. For instance, Cross A demonstrated sex linked genes, which showed that some characteristics are carried down by generation through gender. Not only do sex linked genes determine the sex of the offspring, but they can determine other traits as well because the male carries an X and Y chromosome while the female has two X chromosomes. The data in the table shows an overall even distribution of traits between each sex. For example, in total, there were 130 female red-eyed flies, 135 female white-eyed flies, 154 male red-eyed, and 132 male white-eyed flies.  Most of the numbers of each fly is fairly close in range; however, the data illustrates a sufficiently greater amount of male red eye flies. There are around 20 more male red eyed flies than the others, which illustrates an outlier in the data. The greater amount of red-eyed male flies could be due to the fact that one group could have miscounted, or just that one group had more male red eyes than any other type of fly. Overall, despite the increase in the male red-eye population, the null hypothesis is supported as the sex linked ratio of flies is close to 1:1:1:1. Secondly, Cross B deepened the understanding of a dihybrid cross, which occurs when two different traits are being crossed. Cross B was a cross between the wing type and eye color. The dihybrid cross illustrates complete dominance, which occurs when both parents have the recessive trait, but exhibit the dominant phenotype. Furthermore, a dihybrid cross illustrates independent assortment, which is demonstrated in the 9:3:3:1 ratio of the offspring. This ratio can be seen in the data, as 336 flies were wild type, 117 were red-eyed, vestigial, 102 were sepia eyed, normal winged, and only 42 showed the traits of sepia eyes and vestigial wings. When calculated, the numbers do in fact follow the 9:3:3:1 ratio, which supports the null hypothesis for the dihybrid cross. Lastly, Cross C illustrated a monohybrid cross, which is between one one trait. Cross C had dealt with Sepia versus Wild Type flies, and concluded that Wild Type is dominant over Sepia. When looking at the data table, it can be seen that 263 flies were wild type, while 109 flies were sepia. There were 154 more wild type flies, which shows that wild type is indeed dominant, and the sepia trait is recessive. Also, when looking at the graph, there is a noticeable difference between the two traits, illustrating that there were much more wild type flies produced in the monohybrid cross. Ultimately, the data supported the hypothesis. After looking at both the data tables and graphs, it can be seen that all 3 crosses had similar ratios the those predicted. Also, the chi-squared results had shown little to no significance, as the expected data was very similar to the observed data in the experiment. The experiment conducted was valid due to the fact that many constants were kept, such as: room temperature, living conditions of the flies, and amount of food given to the flies. Since all the flies were treated under the same conditions, the type of cross did in fact cause the change seen in the type of fly produced in the offspring. In like manner, the experiment conducted was reliable as well. The amount of flies in total, 1,520,  exemplifies the reliability of the lab because the more flies that were tested, the more accurate the data becomes. Experimenting with a larger quantity allows for better results. However, during the lab, some sources of error were noted. For example, an unexplainable sudden death of many flies had occured. Many groups had lost much of their offspring, which would have increases the accuracy of the results. To improve upon this error, one could make sure all flies are well fed and held in clean, room temperature vials to ensure the health of the flies. If a follow up experiment was to be conducted, one could study the genes that cause diseases in a fruit fly, as well as a human. By studying these genes, one will learn more about what causes these specific diseases in humans, and how/if they could be prevented. Works Cited