Genetic Research On Fruit Flies- Intro Essay, Research Paper
To do genetic research on a fruit fly one must understand the life cycle of the fruit fly. Also, to do the research, one must know how to: prepare a vial, subculture, isolate virgins, and make crosses with mutant flies. In addition to doing all of the above, one must know how to identify the differences between male and female fruit flies. Finally, a scientist must know how to keep accurate records of all research.
The complete metamorphosis involves four steps. The first step is the egg stage. This stage lasts for only 24 hours. There are two appendages coming out of the egg. The purpose of the appendages is to keep the egg afloat in the liquefied fruit. The egg needs to stay afloat in the fruit because the oxygen is at the top. During this stage embryonic development occurs.
The next stage is the larval stage. This stage has three instars. The main purpose of this stage is for the organism to eat and grow. This is the only growth stage in a fly’s life. The exoskeleton is hard and jointed. When the larva has filled its exoskeleton it molts into the next instar. After the fly molts, it splits the cuticle, and takes on water to stretch the exoskeleton. The larva crawls out of the exoskeleton. The fly grows by replacing the water it took on with cells. When the egg hatches into the first instar the fly is worm-like with a length of one to two millimeters. This instar lasts for two days. The first instar molts into the second instar. The result is a worm-like fly that is two to three millimeters long. The whole process takes two to three days. The second instar then molts into the third instar. In the third instar this worm-like fly is now four millimeters long. This instar also lasts for two days. When this instar ends, the fly is searching for a solid, dry object to cling to.
Once the fly is glued to the object it becomes a pupa. In the pupal stage of life: the cuticle dries and darkens, no feeding occurs, and metamorphosis takes place. This whole process occurs in six days.
The anterior of the pupa case splits open and the adults squeeze out. The primary purpose of this one month stage in life is to reproduce. The exoskeleton of the adult does not grow any bigger. When enclosure is complete, the wings must be inflated or they will harden. About 10 hours after enclosure is complete, the female fly will begin to mate. She will mate frequently throughout her life and lie up to 2000 eggs.
All this research will be done in vials instead of the wild. The preparation of a sterile vial is easy. The first step is to thoroughly clean the vial and stopper in hot soapy water. Once they are clean, they must be dried. The next step is to put an equal part media and water together. Next, eight to ten grains of yeast must be added to the vial. The media is made with starch and other minerals. The purpose of the water is the hydration of the flies and for the yeast. Yeast provides food for the flies. Another role of the yeast is to digest the starches in the media and turn them into glucose. The water then dissolves the glucose. The result of this action is the liquefaction of the media. The final step in the process of making a vial is to label it properly. The label must include name, date type of flies, mods, and teacher.
All the data that is collected during this research will be recorded in lab books for proof of findings. The book will contain six columns. The columns will be labeled date, male wild type, male white eye, female wild type, female white eye, and signatures. All the entries and signatures must be done in ink. Each observations are made involving counting or sexing, the lab book should include the signature of the advisor present during the tests. Any recording that has not been signed will not be accepted. This is one of the most important elements of the project.
To back up all results and provide insurance in case of mistakes, it is good to have more than one vial. The backup vial is called a subculture. When pupa cases begin to accumulate on the side of the vial, it is a good indication that it is time to subculture. The more adults present, the better. A good number to go by is ten. With less than ten, the results will vary.
To subculture flies it is best to follow all the procedures for making a sterile vial. First, open the newly created vial. Then tap the old vial to knock all of the flies away from the stopper and then remove the stopper. Put the vials mouth-to-mouth. The next step is to firmly tap the vials. Not all the flies have to be transferred. Once there are enough flies in the newly created vial replace the stopper. Then, stopper the bottom vial. This easy procedure will be repeated may times throughout the project.
The sexing of fruit flies can be complex at first, but with practice it becomes easier. In order to sex fruit flies, a dissecting microscope is needed. There are four main ways to sex a fruit fly. A non-reliable way is to hold a male next to a female. The male will be slightly smaller. Another way to tell the difference is by the shape of the abdomen. Males have a rounded abdomen, while females have a pointed abdomen. The second best way to sex the flies is by the coloration of the abdomen. Males have solid black abdomens; however, females have stripped abdomens. The best way to sex flies is by looking for sexcombs. Males have them on their forelegs.
In order to ensure a controlled experiment, only virgin flies should be used. The main reason for this is that the female stores sperm from all previous mating and then randomly uses it. If this happens, there is more than one experimental variable. All successful research should be done in a controlled environment so that the genetic relationships can be determined.
When wings become visible on the dorsal surface of the pupa case it is possible that enclosure will occur in a day or two. All the adults must be released no more than ten hours before the planned isolation. If the isolation is planned to be done in the morning, the adults should be released around ten o?clock at night. When the new adults eclose, the vial should be brought to school. The first thing to do is to select and clean an anesthetizer. It is recommended that not more than eight flies be anesthetized at one time. Once all the flies are in the anesthetizer quickly stopper it. Just when the flies stop moving empty them onto a quarter sheet of white paper. Using a dissecting microscope sex the flies. Record all the data and have Mr. Johnston sign the lab book after he verifies the results. Then place the virgins in a sterile vial of media. This time the media only should have one or two grains of yeast. The vial should be horizontal. After all the flies are conscious the vial can be set straight up again.
Once there are ten virgin females, it is time to obtain the mutants from Mr. Johnston. Anesthetizing all the mutants is the next thing to do. Isolate four or five males. Put those males in with the ten virgin females. When the pupa begins to appear, all the adults should be released. Record in the lab book the first day of enclosure. Count, identify, and sex the flies for ten calendar days. This is the F1 generation. Place the first twenty or so adults in a sterile vial. When pupa first appears, release all the adults. Also, record in the lab book the first day of enclosure. After ten calendar days the project is most likely completed.
The mutant type whiter eyes have many similar characteristics with the wild type. For example, both types have wings that extend beyond the edge of the abdomen and then fold flat against it. Also, both types have a tan body with white stripes. The only real difference is that the white eye type has white eyes and the wild type has red eyes.
The criteria for this project sounds intimidating. It appears that many hard skills must be mastered to complete the project. The skills of subculturing, data collection, mutant types, sexing, and crossing can become second nature with much practice.