Name Student ID Page 1 Zoology 470 Exam 2 2014 This exam has 6 pages and a total of 50 points You will have 90 minutes to complete it Answer all short answer questions as briefly as possible Make sure your name and ID number are on all pages 1 3 points Provide concise definitions for each of the following a multicellular rosette Structures formed when cells engage in convergent extension Rosettes form when cells converge and these groupings of cell resolve as a tissue extends A wel studied exam le is during convergent extension of the fly epidermis during germ band extension b ectoderm Most external of the three primary germ layers Ectoderm gives rise to tissues such as epidermis and CNS c reductive cleavage Cleavages in early embryos which partition the same cellular volume into progressively smaller cells without growth 2 Egg activation is known to involve a number of ionic and signal transduction events a 2 points You treat a sea urchin egg with the BMS 354825 whioch inhibits the protein Src and then fertilize it What effects do you expect Explain your reasoning Src is thought to lead to activation of PLCg which in turns leads to calcium release from the ER as part of the calcium wave Blocking Src would block PLC activation leading to lack of calcium release and reduced egg activation and cortical granules release as part of the slow block to polyspermy b 2 points You are testing a new inhibitor of Na H exchangers using sea urchin eggs What effects would this drug be expected to have on a fertilized sea urchin egg Explain your reasoning The Na H exchanger is responsible for the increase in pH after fertilization that leads to maximal macromolecular synthesis Blocking this exchanger would suppress the pH increase thereby suppressing protein synthesis and other macromolecular synthesis 3 Transcription factors can play a powerful role in sex determination a 2 points Sry is crucial for development of male mammals Describe one experiment that demonstrates that Sry is sufficient to confer the male phenotype Transgenic mice carrying an sry transgene who are XX display male characteristics XX mice with a crossover that carries the sry locus onto the pseudoautosomal region of one X chromosome have the same phenotype Name Student ID Page 2 3 cont b 1 point Androgen insensitivity syndrome results from mutations in a hormone receptor which is required for cells to respond to testosterone Where is the primary site of action of this receptor once it has bound testosterone Primary site of action within the cell nucleus c 1 point Female mammals produce the sex hormone estrogen from another sex hormone What is this hormone Hormone testosterone 4 9 points Circle true T or false F for each of the following T RNA helicases are a conserved component of germ plasm in many animal embryos T Protein gradients as a patterning mechanism are possible in Drosophila because the early embryo is syncytial oskar would be expected to be a zygotically acting gene since it encodes a gene product required for germ cell formation in Drosophila embryos maternally acting F F F T F T The expression of protein products from a gene can be regulated at the level of transcription or translation but not both False hunchback is a good example in which both happen Presumptive endodermal cells in C elegans are internalized via delamination ingression Transcription factors can increase or decrease the amount of transcripts produced from the genes they regulate Anti M llerian hormone would be expected to be expressed at a higher level in a female mouse fetus than in a male mouse fetus opposite is true Normal zebrafish primordial germ cells placed into an embryo lacking the function of the chemokine SDF 1 would be expected to migrate abnormally T MicroRNAs are short RNAs that can regulate the translation of mRNAs F Removing the RNA polymerase binding site from the even skipped gene would not be expected to disrupt the transcription of even skipped since its transcription is tightly controlled RNA pol is generally needed for genes to be transcribed Removing the 3 untranslated region from the oskar RNA would be expected to affect where it is localized in the oocyte When the histones associated with a region of chromatin are heavily acetylated transcription of the associated gene would be more likely than when the histones are not acetylated Elongation of the archenteron in sea urchins occurs via convergent extension T T T T T T F F Sea urchins are thought to be more closely related to chordates than arthropods because they are deuterostomes Alternative splicing leads to the production of mRNAs with slightly different coding regions leading to proteins with slightly different amino acid sequence Ventral furrow formation during Drosophila gastrulation occur primarily by invagination Transplantation of primary mesenchyme cells from a normal embryo into an embryo whose dorsal ventral axis is perturbed would be expected to make a normal skeleton radialized When primary mesenchyme cells ingress they would be expected to show in increase in cadherin based adhesion decrease Name Student ID Page 3 5 Answer each of the following questions which relate to cleavage in early embryos a 1 point You observe a sea urchin zygote shown with RNA that encodes a fluorescent protein that acts as a reporter of Rho activity The zygote then goes on begin first cleavage as shown Assuming that the zygote on the left is drawn at a time immediately before the embryo on the right draw the region within the embryo on the left where you saw elevated Rho activity prior b 1 point What type of yolk distribution did the one celled zygote have that gave rise to the embryo at the right Type of yolk distribution mesolecithal c 2 points You work in Rick Elinson s lab at the University of Toronto You discover a frog species whose eggs have 1000 times as much yolk as the eggs of Xenopus laevis Before you look at a embryos of the new species Rick asks you to predict the likelihood of complete cleavage in the new species How would you repsond Explain your reasoning It would be much less likely to have complete cleavage Teolecithal eggs undergo meroblastic cleavage e g bird reptile eggs 6 2 points Germ plasm is a specialized type of cytoplasm found in many metazoans multicellular animals Describe one experiment that shows that germ plasm acts as a localized determinant that is sufficient for germ cell formation in Drosophila You need not describe detailed technical aspects