Paper1InClassQ&A

Questions on ced-9 paper - answers Class 6 Please discuss these questions with your group (and a nearby LA or TA if you like), hopefully until the answers are clear. Then take the last 15 minutes of class time to write on this sheet your own answers, in your own words, using the reverse side of the page as necessary. When you are done, give your paper to a TA or LA. Answers are worth 10 points total. 1. (2) Explain the rationale of looking for intragenic (cis-dominant) suppressors of n1950 to obtain ced-9(lf) mutations. The gf phenotype must result from a form of the ced-9 protein with altered activity. A lf mutation in the mutant ced-9(gf) gene will eliminate some or all protein activity, and therefore suppress the gf phenotype. (It may also cause a different, possibly lethal defective phenotype, so appropriate approach must be used, as in Fig. 1 2. (1) In general, what is the phenotype resulting from ced-9(lf) mutations Ectopic cell death a lot of cells die that normally do not. 3. (3) In Table 1, explain why, in double mutants for egl-1 and either ced-3(lf), ced-4(lf), or ced-9(gf) mutations, no worms are missing HSNs, while in egl-1 single mutants, 99 of the worms are missing HSNs. What does this imply about how these genes work together Are they in a pathway If so, what is the order of egl-1 with respect to the ceds egl-1 mutations cause HSNs in hermaphrodites to die (activates the cell death pathway in HSNs), causing an egg laying defect. Any one of the three ced mutants eliminates all cell death, so suppresses the egl-1 effect. This suggests that egl-1 and the ceds are in the same pathway, and that egl-1 is upstream of them (e.g. egl-1 normal function is to turn off ced-9 in HSNs in hermaphrodites. 4. (4) Which data in the paper indicate that ced-9 functions upstream of ced-3 and ced-4 Cite those data specifically (Table and line number), explain them briefly, and explain why they indicate this conclusion. Table 3, lines 2, 3, 7 i.e. the double mutant phenotypes, compared to ced-9(lf) alone. The finding that ced-3 or ced-4 lf mutations suppress the ced-9(lf) phenotype indicates that ced-9 is probably upstream in the same pathway. MCDB 4650 DEVELOPMENTAL BIOLOGY Spring 2006 Name ___________________________________________