ex3_2006_key - Name Student ID Page 1 Zoology 470 Exam#3...

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Unformatted text preview: Name: ______________________________________ Student ID:________________________ Page 1 Zoology 470 - Exam #3 – 2006 This exam has 7 pages and a total of 50 points . You will have 120 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. Provide concise definitions for each of the following ( 6 points ) a. nodal cilium: "9 + 0" cilia that are involved in establishing left-axis asymmetries in vertebrate embryos. Loss of nodal ciliary function results in situs inversus. b. neuropore: Openings at the anterior and posterior ends of the neural tube in chordates. Failure to close the anterior neuropore results in anencephaly; failure to close the posterior neuropore results in spina bifida. c. chorionic villus biopsy (sampling): Removal of placental tissue (chorionic villi) for the purpose of genetic testing in human fetuses. d. sclerotome: Somite derivative that gives rise to mesenchymal cells that form the vertebral column. e. netrin: Neuronal guidance molecule that acts as a chemoattractant for commissural axons in the vertebrate spinal cord, and can also act as a repellant for other neuronal cells types. Netrins homologues are found in a wide range of animal embryos, including C. elegans. f. metamerism: Phenomenon in animal embryos involving segmental repetition of body parts. Examples include segmentation in arthropods, and somites, rhombomeres, and the vertebral column in vertebrates. 2. The unrestricted potency of cells in vertebrate embryos is an important feature of their early development. a. Neural crest cells and their progeny appear to be pluripotent. Describe one piece of evidence that neural crest cells are pluripotent ( 1 point ) Possibilities: (1) Lineage tracer injections into single NCs result in multiple tissues types containing label. (2) Treating NCs in culture with various growth factors (e.g., nerve growth factor, retinoic acid, etc.) results in different differentiated derivatives. b. Blastomeres in early mammalian embryos are totipotent, allowing for preimplantation genetic diagnosis (PGD). At what stage of early embryonic development is this procedure typically performed? ( 1 point ) Prior to compaction, usually at the 8-cell stage Name: ______________________________________ Student ID:________________________ Page 2 2 (cont) c. In PGD, material that possesses an undesirable genetic constitution is routinely discarded. You are called in to counsel a second family that thinks reproductive technologies are ethically permissible, but that is opposed to any procedure that results in intentional destruction of zygotes. Would this family be opposed to discarding either or both of the cells shown in the diagram? State your reasoning clearly ( 1 point )....
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ex3_2006_key - Name Student ID Page 1 Zoology 470 Exam#3...

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