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Drosophila Melangaster, more commonly known as the fruit fly, is the basis of this lab activity. In the process of this lab, we saw a total of three generations of flies. First, we start out with a parent generation of one male and one female. After identifying the traits of each homozygous parent, we removed them from the vial, in order to keep them from reproducing with their children. Next, because of the breeding of these two flies, we had offspring, whose traits we then mapped after they had developed from the pupa. To do this, we had to keep the flies under the microscope without them flying away. We used Fly Nap , a product designed to temporarily paralyze the flies, just long enough for us to determine the gender and genotype of each fly. After inspecting the flies, they were killed, either by releasing them outside or placing them into a jar of liquid. After the F1 generation was developed, counted, an analyzed, we were to remove to or three flies from that generation and place them in a new vial. This new generation that is to be produced from the F1 generation is the F generation, the grandsons and granddaughters of the original parent generation. This experiment was designed to examine the parent generation and its offspring, and see how genotypes, as well as phenotype of sex-liked traits are passed through generations.
The life cycle of a fruit fly, also known as complete metamorphosis (Figure A), is divided into four stages, egg, larva, pupa, and adult. Drosophila Melangaster will produce new adults in two weeks, eight days in the egg and larval stages, and six days in the pupal stage. Twenty-four hours after the egg is laid, the larval hatches. The larva has two molting (shedding) periods; during which the cuticle (outer portion of the exoskeleton), mouth, hooks and spiracles are shed. This larva is called an instar during the periods of growth before and after molting. Thus, the fruit fly has three instars. The puparium develops from the third instar, which becomes which becomes hard texture and dark in color. Upon completion of metamorphosis, the adult forces its way through the operculum (end) of the puparium. Initially the fruit fly appears light in color with a long abdomen and unexpanded wings. In just a few hours the fly gets darker in color, rounder in the abdomen and extends its wings. A female fruit fly can store sperm after a single insemination ad use it for many reproductions. The sperm the female obtains is used randomly (not in the order they were obtained) to fertilize the eggs as they were laid. This process, complete metamorphosis, is different than incomplete because of the resting stages during complete metamorphosis. For example, caterpillars are transformed in a cocoon, and fruit flies change in the pupa stage. Also, in incomplete metamorphosis, there is a gradual change in appearance such as the wing pads grow longer with each molt, and eventually into wings in the adult. In incomplete metamorphosis the immature forms are called nymphs, which generally have the same food source as the adult.
The process of anesthetizing flies uses a product known as Fly Nap . This product allows us to look at flies under the microscope without them flying away. In order to correctly utilize the Fly Nap , place some on one side of a sponge stopper. Then, gently tap the vial in which the desired flies are in, which should knock them to the bottom. Quickly remove the stopper, then place an inverted vial on top of that vial without allowing any flies to escape, the flies should rise into the inverted vial. Next, promptly place the stopper that has the Fly Nap on it into the vial containing the flies. In about one minute the flies should be temporarily paralyzed; this will allow you to look at the flies under the microscope without them flying away.
Distinguishing sex between the male and the female can be noticed when looking under a microscope. The most easily identifiable difference is the coloring of the rear. The male has heavy pigmentation on the entire posterior part of the abdomen, and has two bands frontal, while the female has five bands of color along the entire abdomen. The problem with this type of distinction is the inability to see color in newly emerged flies, however, in mature flies, the difference is clear. Another difference is the shape of the posterior tip (Figure C). In females, the tip is slightly pointed, while in males the tip is rounded. Finally, the males have a pair of sex combs (Figure B), located on each leg, which are used to grasp onto females during intercourse.
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In our experiment, there were three traits that could vary in the flies sex, type of wing, and the eye color. For this lab, the following labels were used to show the genotype behind each phenotype
In sexual reproduction, the genes that are produced by the male are the genes that determine the gender of the offspring. The male can generate either a XY (male), or XX (female) sperm. If the Y chromosome is combined with the X chromosome of the female, the offspring will be male. However, if the male provides the female with his X chromosome, the offspring will be female.
Certain physical traits, or phenotype match up with certain genotypes. In this lab, long wings are dominant, which means that if a L gene is passed from either parent to the offspring, that particular child will have long wings. If both parents transmit the gene, the trait the offspring will be known as a homozygous for that trait (LL). However, if only one parent passes on the gene, the child is known as a hybrid, or heterozygous (Ll).
Also, in order for a child to have short wings, the parents must both give the recessive trait of short wings to the child, that making the child homozygous (ll) for that characteristic.
A mainly significant type of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked. A large part of sex linkage has to do with the fact that a single chromosome determines several genes. This is because the X chromosome is longer and straighter than the Y chromosome (Figure D), and occasionally has genes that are not always on the Y chromosome. Because the blending of these chromosomes decides the gender of the offspring, in addition to the eyes, the color of the eyes is identified as a sex-linked trait. For instance, if a male received an X chromosome containing the gene for white eyes, he will have white eyes, because the Y chromosome does not carry that trait and will then have no effect on that specific characteristic. On the other hand, if a fly is female, both X chromosomes must carry the white-eye gene in order for her to have white eyes. That female will only be that carrier of that gene, and pass that gene on to their offspring. This relationship linking the gender along with attributes of the fly is recognized as sex linkage.For this experiment, it was known that the traits for the parent (P) generation were homozygous. Having that information, we were able to identify our parent generation's genotype, after examining their phenotype. Our males were short winged, red eyed (XYll), while our females were long winged, red eyed (XXLL). Using this data, we were able to predict the genotypes and phenotypes of the F1 generation using a Punnet square (Figure E). By studying this information, it is observed that our estimation is that half of the F1 generation will be males with red eyes and heterozygous long wings, while the other half will be females with red eyes and heterozygous long wings.
By comparing our approximation with our actual F1 generation, we found out that our presumption was almost identical to the actual offspring (Figure F).
Then, we used the genotypes of our F1 generation to predict their children, or the F generation (Figure G).
Using the Punnet square above, we made the following predictions for the genotypes of the F generation
Then, using the genotypes, we predicted the phenotypes
Unfortunately, we were not able to test our predictions; the F fruit flies did not hatch in time for us to be able to include them in our report.
While working on this lab, there was a large margin for error and it is quite possible that mistakes occurred. First of all, when transporting flies from one container to another either when examining them or otherwise, it is probable that some flies flew out of the vial. This problem could change the number of parents and also change the results of the following generation. Also, when breeding the flies, it is likely that some flies from the earlier generation could have stayed in the vial, and have not been removed. This would cause the parents to mate with their children, and this inbreeding could modify the expected results. Another problem that existed was the paralyzed flies falling back into the food after being examined under the microscope. This would lead to a death of that fly and change the counting of that generation and also the following generation. Another obvious problem could be the miscounting of male and female flies by mixing them up, or just not counting certain flies at all. Either one of these problems or a mixture of these troubles could considerably change the outcome of the lab. - Day 1 My partner and I practiced examining the flies, as well as distinguishing between the males and the females. Also, proper techniques on how to use Fly Nap as well as how to use the soft bristled brush to manipulate the flies under the microscope were explored.
- Day We received the parent generation and examined the phenotype plus the genotype for future mapping. We were told that each fly was homozygous for the purpose of Punnet squares. We removed the parents from the vial and observed the developing larva.
- Day We both counted the flies of each sex and phenotype as well as compared that count to our predictions.
- Day 4 My partner and I continued to count the F1 generation and added the number of the rest of the flies to the previously counted number.
- Day 5 The final counting of the F1 generation was complete, the phenotypes and genotypes of those flies were compared to our predictions. We also placed two adults from each sex into a new vial to prepare for the second generation (F).
- Day 6, 7, 8 Digital pictures of us were taken. This report was written. Unfortunately, The F generation did not hatch in time for us to compare them to our predictions.
References
- http//www.flushing.k1.mi.us/srhigh/tippettl/genetics/ins.html
- http//bioweb.uwlax.edu/bionet/Genetics/Fly_Genetics/fly_genetics.html
- http//www.central.edu/homepages/liedlb/genetics/FlyInfo.PDF
- http//www.accessexcellence.com/AE/AEPC/WWC/14/life_cycle.html
- Carolina Drosophila Manual
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