Unformatted text preview: Name: ______________________________________ Student ID:________________________ Page 1 Zoology 470 - Exam #2 – 2008 This exam has 5 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. You will receive 1 point for doing so. 1. Provide concise definitions for each of the following (5 points) a. Wolffian duct: b. midblastula transition: c. ectoderm: d. contractile ring: e. invagination: 2. Complete the following table referring to cleavage patterns in early embryos of various animals (4 points) Animal Squid (cephalod mollusk) Chimpanzee (mammal) Earthworm (annelid) Salamander (amphibian) 3. Transcription factors can play a powerful role in the differentiation of tissues in embryos. a. The pax-6 family of proteins are important for the development of eye structures. Describe one experiment that demonstrates a pax-6 family member is necessary for eye development (2 points): isolecithal holoblastic Yolk Distribution Completeness of Cleavage meroblastic rotational Orientation of cleavages b. Sry is crucial for development of male mammals. Describe one experiment that demonstrates that Sry is sufficient to confer the male phenotype (2 points): Name: ______________________________________ Student ID:________________________ Page 2 4. Circle true (T) or false (F) for each of the following (7 points) TF TF TF TF TF TF TF TF TF TF TF TF TF TF RNA helicases are a conserved component of germ plasm in many animal embryos 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 Genes can be transcriptionally regulated or translationally regulated, but not bo th Presumptive endodermal cells in C. elegans are internalized via convergent extension Transcription factors can increase or decrease the amount of transcripts produced from the genes they regulate Testosterone is made in both male and female mammals Normal zebrafish primordial germ cells placed into an embryo lacking the function of the chemokine, SDF-1, would be expected to migrate abnormally into the gonadal ridge MicroRNAs are short RNAs that can regulate the translation of mRNAs 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. Removing the 3'-untranslated region from the oskar RNA would be expected to affect where it is localized in the oocyte If a frog is discovered whose oocytes have 100 times the yolk found in a Xenopus oocyte, it would be less likely to undergo complete cleavage, and its blastocoel would be expected to be less centrally located than in Xenopus The midblastula transition in Xenopus would be delayed in an embryo derived from an oocyte with a much less than the normal amount of cytoplasm Treating a fertilized sea urchin egg immediately after sperm penetration with a microtubule poison would block pronuclear migration 5. Your friend is working in a laboratory that studies early blastomere specification in a nematode species closely related to C. elegans. Assume all cells in the early embryo have the same names as in C. elegans. Diagrams of the one-, two-, and four-cell embryo of the new species are shown for reference.
anterior posterior a. Your friend has developed a way to see where the sperm entered the oocyte at fertilization, and uses this technique in the new species. Assuming the same cues operate in the new species, at which end (left or right) of the oocyte did the sperm enter, if the zygote (P0) is shown in the same position as the oocyte? (1 point) Location where sperm entered (left/right): ____________________________________ Name: ______________________________________ Student ID:________________________ Page 3 5 (cont) b. Your friend goes on to discover a new mex gene, which she has named Tex mex. In the absence of Tex mex function, SKINHEAD protein localization is abnormal. If Tex mex is similar to MEX proteins in C. elegans in function, in which cell(s) of the 2-cell embryo would you expect to find SKINHEAD if the embryo lacks TEX MEX protein? State your reasoning (2 points) c. RNA-mediated interference (RNAi) works well in the new species, so your friend performs RNAi against the Wnt gene most similar to mom-2 in C. elegans, which your friend names Wntergreen (your friend has a penchant for goofy names). What major organ/tissue do you expect to be absent when the function of Wntergreen is removed? Clearly state your reasoning (2 points) 6. You are studying sex determination and dosage compensation in mammals. a. In a female mouse embryo that is homozygous for a loss-of-function mutation in the Xist gene, what well-known structures observable under an ordinary microscope would be absent from the cells of the embryo (1 point)? Structure predicted to be absent: ______________________ b. You develop a new tool that allows you to watch the localization of Xist transcripts in living cells of the very early mouse embryo. Using the diagram below, indicate where Xist transcripts would be found, if the indicated X chromosome becomes inactivated (1 point) X chromosome will become inactivated 7. In an episode of the X-Files called "Postmodern Prometheus", an evil developmental biologist is experimenting with a human Hox gene most similar to the Drosophila homeotic gene proboscipedia. Mulder is unfamiliar with homeotic genes, and asks for an explanation from Scully, who does her best to remember her undergraduate biology classes. Name two key features of all homeotic genes that Scully should explain to Mulder (4 points): Feature #1: Feature #2: Name: ______________________________________ Student ID:________________________ Page 4 8. The following questions refer to the functioning of the segment polarity genes in Drosophila. a. Segment polarity genes are thought to be regulated heavily by the products of the pair rule genes. What kinds of proteins are encoded by the pair rule genes? (1 point) Kind of protein: ________________________________ b.. Armadillo, the fly β-catenin, is a segment polarity gene. How would the levels of armadillo protein in the cytoplasm of cells making engrailed protein compare with levels of cytoplasmic armadillo in other cells? Explain your answer (3 points) c. Eric Wieschaus and Christiane Nüsslein-Volhard used a convenient, easily visible feature of the Drosophila embryo to screen for segmentation mutants. What was this feature? (1 point) Visible feature: ________________________________ 9. Maternal polarity gene products dramatically affect anterior and posterior development in Drosophila. Answer the following questions regarding how these proteins act. Use the provided diagrams to indicate the expected expression of the molecule in each case. a. Indicate the expression pattern of caudal protein in an embryo derived from a bicoid loss-offunction mutant mother (1 point)
Anterior Posterior b. Indicate the expression pattern of maternal hunchback mRNA in an embryo derived from a bicoid loss-of-function mutant mother (1 point)
Anterior Posterior c. Indicate the expression pattern of nanos mRNA when the anterior end of the oocyte is pricked with a needle and cytoplasm is allowed to ooze out (1 point)
Anterior Posterior d. Indicate how the pattern of even-skipped expression (normal pattern is shown at the left) would be altered in embryos from a mother expressing 4 copies of the bicoid gene (1 point)
Normal eve pattern Anterior Posterior eve pattern in embryo from 4x bicoid mother Anterior Posterior Name: ______________________________________ Student ID:________________________ Page 5 10. Pair rule genes in Drosophila are crucial for the proper segmentation of the embryo. a. What key feature of the expression pattern of gap proteins is important for regulating the expression of pair rule genes? (2 points) b. Certain mutations in the pair rule gene even-skipped result in the loss of one or two specific stripes of even-skipped expression in the embryo. What defect(s) in the mutated even-skipped gene could account for this pattern of even-skipped expression? (2 points) 11. Your friend, Rob Maxson, is studying an Antarctic sea urchin at McMurdo Station. a. Rob wants to show that micromeres in the Antarctic species produce inductive signals similar to those in other sea urchins. Assuming all experiments perform ed in other species are possible, describe an experiment that would show the micromeres in the new species behave in a manner similar to other species (2 point) b. Rob now performs a molecular test for proteins that are in the nucleus of micromeres in the new species. Assuming he can clone the Antarctic version of any gene found in well-studied sea urchins or make any other reagent he needs, name one molecule that Rob might expect to be at high levels in micromeres. (1 point) Name of molecule found in nuclei of micromeres at high levels:__________________________ c. You are a physiologist working with Rob in Antarctica, and you are testing a new inhibitor of Na+/H+ exchangers using sea urchin eggs. What effects would this drug be expected to have on fertilized sea urchin eggs? Explain your reasoning (2 points) ...
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