bicd130_06_finalkey

bicd130_06_finalkey - BICD 130 - Embryos, Genes, and...

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BICD 130 — Embryos, Genes, and Development Winter 2006 Final Exam (Four parts, 200 points total) ANSWER KEY ______________________________________________________ Please PRINT your name here Please write your answers in ink . Requests for regrades will not be considered for exams done in pencil. Part I (74 pts.)________________________ Part II (28 pts.)________________________ Part III (68 pts.)_______________________ Part IV (30 pts.)_______________________
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I. (72 pts.) 1. (8 pts.) Signaling via two pathways is responsible for dorsal-ventral patterning of the vertebrate neural tube. What are the two pathways? Which one acts primarily on the dorsal neural tube and which on the ventral neural tube? What tissue is the original source of each signal? What tissue becomes the secondary signaling center in each case? BMP/TGF-B pathway 1 -acts dorsally 1 Shh pathway 1 - acts ventrally 1 BMP signal originates in ectoderm 1 / epidermis 1 Secondary BMP signalling center in roofplate 1 / Dorsal neural tube or neural tube 0.5 Shh Signal originates in notochord 1 / mesoderm 0.5 2nd signal center in floorplate 1 / ventral neural tube or neural tube 0.5 Diagrammatic answers must be fully labeled and clear for points to be awarded. D-V orientation should be labeled. 2. (8 pts.) Initially both the Müllerian and Wolffian ducts are formed in both males and females. Explain specifically how the hormones produced by the ovaries or testes determine which duct(s) will be maintained in each sex. Also name the structures eventually derived from each duct. Anti-Mullerian hormone AMH 1 -secreted by Sertoli cells 1 -degrades mullerian duct in males 1 Testosterone in males 1 -secreted by Leydig cells 1 -sustain Wolffian ducts in males, Wolffian ducts become epidydimis, vas deferens, seminal vesicles 1 (name at least one) / sperm ducts 0.5 -no Wolffian ducts in females due to absence of testosterone 1 In females Mullerian duct becomes Fallopian tubes, uterus, cervix, upper vagina 1 (minimum of one structure must be named) Incorrect answers: Wolffian ducts give rise to scrotum, penis, prostate, ovary, testes -0.5
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3. (8 pts.) Referring to the development of the chick forelimb, what is the expected outcome of the following experimental manipulations? (a) Removal of the AER No limb development occurs. (2) (b) Replacement of forelimb mesoderm with leg mesoderm Proximal wing structure and distal leg structures forms (2) (c) Replacement of the AER with an FGF-soaked bead Normal Limb development (2) (d) Implantation of a Sonic hedgehog-expressing cell pellet into the anterior portion of the limb bud Mirror image duplication of digits (2) 4. (6 pts.) Treatment of fertilized Xenopus eggs with UV light leads to the development of “ventralized” embryos by preventing the cortical rotation. Treatment with high concentrations of lithium chloride (LiCl) has the opposite effect—development of excess dorsal tissue. LiCl treatment can even partially rescue UV-irradiated embryos, in effect
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bicd130_06_finalkey - BICD 130 - Embryos, Genes, and...

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