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Baker Lacey Bio Lab Section 006 6 December 2006 Title Studies on an Unknown Cross in the F1 Generation of Drosophila Introduction In this Genetics lab, we studied Mendelian Genetics through a common insect, normally regarded as a household pest--the fruit fly. "Drosophila Melanogaster, the ,,common or ,,vinegar fruit fly....is not an agricultural pest...but a ,,model organism." (Vieyra 5-1) It is very useful in experiments because it has a short life span, its cheap to buy and obviously very small. It is often used in the study of genetics because they only have four chromosomes, which makes it easy to see changes in the phenotypes, which are the physical attributes, because there are only a limited number of them. In addition, they live for "over two weeks in the wild and up to six months in a lab". (Vieyra 5-1) They also reproduce very quickly. "Males are easily distinguished from females based on color differences; males have a distinct black patch at the abdomen." (Wikipedia) My hypothesis for this experiment was that the chi squared test and the Punnett Square would show the F1 generation as heterozygous. In this experiment, we bred drosophila with unknown genotypes, which are the actual genes an organism, to see what the phenotype of their offspring would be. The F1 generation as well as the parent generations were unknown. The offspring that we studied from the F1 generation was the F2 generation. "The fruitfly, Drosophila melanogaster, has been of central importance in analysing the mechanics of cellular processes. Classic forward genetic screens in the fly have identified many of the genes that define critical cell signaling pathways, for example." For this experiment, we had to have the basic knowledge of Punnett Squares. A Punnett Square, by definition, is "a diagram used in the study of inheritance to show the results of random fertilization in genetic crosses." (Campbell Glossary) Our Punnett Square was a dihybrid cross because our drosophila had two unknown traits. A dihybrid cross looks at two traits at a time, so in our experiment, we looked at the traits of vestigial wings versus normal wings, and ebony bodies versus normal colored bodies. " We formed one Punnett Square showed below: VE VE Ve vE Ve VVEE VVEe VvEE VvEe Ve VVEe Vvee VvEe Vvee vE VvEE VvEe vvEE vvEe ve VvEe Vvee vvEe vvee Doing this dihybrid cross showed us that the phenotypic ratio was 9:3:3:1, meaning that nine would show both dominant traits, three would be heterozygous for one trait, three would be heterozygous for the other trait, and one would be homozygous recessive. The F1 generation for our flies had normal wings and normal colored bodies, meaning that they had no mutations. However, their offspring DID show mutations, us telling that the F1 generation was heterozygous for both traits. We observed the following about the number of flies observed by different groups in class shown below: Phenotype Normal/Normal Normal/Ebony Vestigial/Ebony Vestigial/Ebony Total O 186 45 46 17 294 Methods In this experiment, we bred Drosophila melanogaster to see the phenotypic ratios of the offspring. We started by giving them a chemical much like ether called ,,Fly Nap. Our objective was to keep the flies alive for as long as possible, so we placed the tube with the F1 generation drosophila on its side. We sorted three female and two male drosophila from the bunch to be put into a vial for our individual group. We also put yeast in our vial for the flies to eat during the two week span that we allowed them to reproduce. Two weeks later, we took the vials back out and saw that of course, the flies had multiplied immensely. We put the flies back to sleep with the ,,Fly Nap again, and looked at them under the microscope to see if there were any new phenotypes in the F2 generation. We found new phenotypes, which were ebony (dark) colored bodies and vestigial (shriveled) wings. Results After the flies reproduced, we had to analyze what we found. Our results came close to that of a 9:3:3:1 ratio (since its very hard to get an exact ratio), and we found out that the F1 generation was heterozygous. The chart below shows what we found and the ratios: Phenotype Normal/Normal Normal/Ebony Vestigial/Normal Vestigial/Ebony Total O E O-E (O-E)^2 186 165 21 441 45 55 -10 100 1.82 46 55 -9 81 1.47 17 18 -1 1 .05 294 293 NA NA 6.015 (O-E)^2/E 2.67 Chi Squared Discussion We did a Chi Square test to see how close to the 9:3:3:1 ratio our results were. "We use the chi square test to determine how closely our data matches our expectations." (Vieyra 10-4) Apparently, if the value of the test is below 7.28, then the results are moderately accurate. Our class value was 6.015, which tells us that our results of the F2 generation were very close to the original 9:3:3:1, which basically proves my hypothesis accurate. In my opinion, our experiment was a success, because we didnt mess anything up or kill the flies. Resources Campbell, Neil, and Jane Reece. Biology 7th Edition. San Francisco: Pearson Education Inc. Vieyra, Michelle, and Laurel Hester. Biology 101 Laboratory Manual. Plymouth, MI: Hayden-McNeil Publishing, 2006 Wikipedia, the Free Encyclopedia. Wikimedia Foundation Inc. 4 December 2006 http://en.wikipedia.org/wiki/Drosophila_melanogaster Besjovec, A. Flying at the head of the pack: Wnt biology in Drosophila. Internet; PubMed. 4 December 2006 http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt =AbstractPlus&list_uids=17143288&query_hl=1&itool=pubmed_docsum ... View Full Document

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