Exam2questions - Name: _ 7.06 Cell Biology EXAM #2 March...

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Name: _____________________________ 7.06 Cell Biology EXAM #2 March 17, 2005 This is an open book exam, and you are allowed access to books, a calculator, and notes but not computers or any other types of electronic devices. Please write your answers in pen (not pencil) to the questions in the space allotted. Please write only on the FRONT SIDE of each sheet. And be sure to put your name on each page in case they become separated! Remember that we will Xerox all of the exams. Good luck! Question 1. 20 pts __________ Question 2. 18 pts __________ Question 3. 22 pts __________ Question 4. 20 pts __________ Question 5. 20 pts __________ 1
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Name: _____________________________ Question 1. (20 points) Many neurons from one side of the body send out projections that cross to the other side of the body. You are interested in the development of these “midline crossings” and decide to study them in the fruit fly D. melanogaster . In particular you want to identify factors that prevent neurons from re-crossing the midline once the neuron has crossed the midline, known as repulsion of axons from the midline. You screen for mutant flies that have an abnormally high or abnormally low number of midline crossings relative to wild-type flies (which have a certain set number of midline crossings). You name your mutants xdf1- , xdf2- , xdf3- , and xdf4 * (where a minus sign denotes a recessive loss of function mutation and a star denotes a mutation that causes a dominant phenotype due to constitutive activity of the gene product). The corresponding wild-type proteins are referred to as XDF1, XDF2, XDF3, and XDF4. The following is a list of the single mutant phenotypes you obtain: (Note that the flies are homozygous mutants for all mutations listed.) xdf1- high # of crossings xdf2- high # of crossings xdf3- low # of crossings xdf4* low # of crossings To order the genes into a pathway you analyze the phenotype of various double mutants. These are the results you obtain: xdf1-/xdf3- low # of crossings xdf1-/xdf4* high # of crossings xdf2-/xdf3- low # of crossings xdf2-/xdf4* low # of crossings xdf3-/xdf4* low # of crossings (a, 8 pts) Write out the linear arrangement of the signaling pathway that leads to midline crossing. Your model should show the order of the genes, and should use positive arrows ( ) or negative arrows ( ----] ) to indicate the relationship between the genes. In your model, include only the following: wild-type XDF1, XDF2, XDF3, XDF4 and the output “midline crossings.” 2
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Name: _____________________________ You next decide to study the molecular interactions between XDF proteins and perform co-immunoprecipitation experiments from Drosophila neurons with the following Western Blot results: Lane 1 2 3 4 5 6 7 IP antibody XDF1 XDF2 XDF2 XDF4 XDF1 XDF4 XDF1 Blot antibody: XDF2 XDF2 XDF1 XDF4 XDF1 XDF1 XDF4 (b, 2 pts) What conclusion would you draw from these results with respect to XDF4 and XDF1?
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Exam2questions - Name: _ 7.06 Cell Biology EXAM #2 March...

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