This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Zoo 470 2008 Problem Set #1 Page 1 Problem Set #1 Polar Body Biopsy and Genetic Diagnosis Zoology 470 Spring 2008 20 Points Total Problem Set Guidelines 1. Due date: This problem set is due by 5 pm on Friday, February 22, 2008. It may be submitted either in class or to the mailbox of the course TA, Allison Lynch, in the Zoology Research Building. 2. Sources: You may use any sources at your disposal to answer the following questions. Legitimate sources include classmates, knowledgeable friends and colleagues, written documents, and any other scientific resources you find useful. If you work with other classmates on this problem set, we ask that you list the other students with whom you worked to answer these questions. Although you may discuss these questions as part of a group, you are expected to answer the questions as an individual. If you believe that published references will help you answer these questions, you may cite those references. However, citation of additional references is not required, nor is it expected. 3. Answering the questions: Brief but complete answers should be written in the space provided. If you find it helpful, feel free to include diagrams in your answers. You need only turn in your answers on pages 2 & 3. Necessary information: All of the information and techniques needed to answer the questions on p. 2-3 have been presented in class, or are to be found in Gilbert's Developmental Biology, or in your reading packet.. This problem set involves polar body biopsy, which is now being used in preimplantation genetic diagnosis. You will be asked to draw on you knowledge of meiosis from previous courses, your knowledge of mammalian fertilization, and your knowledge of molecular techniques to answer the questions on the problem set. This exercise also gives you practice in interpreting nontechnical articles on the popular press that relate to developmental biology. Problem Statement Dr. Yuri Verlinsky and colleagues at the Reproductive Genetics Institute in Chicago have developed refined techniques to perform preimplantation genetic diagnosis (PGD). PGD is a term used to describe genetic testing performed on oocytes or embryos prior to implantation. In the accompanying CBS News report from 2002, Dr. Verlinsky and colleagues used PGD in conjunction with a woman heterozygous for a mutation that invariably leads to early-onset Alzheimer's disease (a dominant mutation in the amyloid precursor protein, or APP, gene). A popular description of their technique, which involved polar body removal and testing, is provided in the diagram from the Chicago Tribune on p. 5 of this problem set. Zoo 470 2008 Problem Set #1 Page 2 Name:________________________________ Student Number:__________________ If you worked in a group, other collaborators: _____________________________________________ Answer the following questions regarding the Verlinsky polar body biopsy technique (20 points total): 1. As stated in the Tribune graphic, part of in vitro fertilization (IVF) procedures, it is common practice to stimulate production of more than one oocyte using "drugs" (more technically called "superovulation"). Name one hormone whose synthetic counterparts you would expect to be found in such "drugs" (2 points) Hormone: __________________________________ 2. The Chicago Tribune diagram states that "doctors reproduce the DNA within the chromosomes". What molecular biology technique would likely have been performed to "reproduce the DNA" from polar bodies? (2 points) Technique: _________________________________ 3. Based on Step 3 of the procedure as described in the Chicago Tribune diagram, genetic testing was performed involving "genes". In fact, the published paper states that the presence of a particular restriction site (a unique sequence that can only be cut by a specific restriction enzyme) was used to assess the presence or absence of a sequence associated with the dominant APP mutation. A portion of the data they presented is shown in Figure 1, which is a type of blot:
Figure 1 The first and second polar bodies were biopsied, DNA was obtained, and the DNA was digested with restriction enzymes. DNA samples derived were analyzed for the presence of normal and APP mutant fragments. If the latter are present in one or more copies of the APP gene, the patient will eventually develop early onset Alzheimer's disease. Note: Oocyte #1 was discarded. Oocytes 2 & 3 were used for transfer into the mother a. What technique sis used to separate the DNA fragments as shown in the blot? (1 point) Technique: __________________________ b. What type of blot is this? (1 point) Type of blot: __________________________ Zoo 470 2008 Problem Set #1 Page 3 Name:________________________________ Student Number:__________________ 3 (cont) b. Although explained somewhat poorly in Step 3 in the Tribune diagram, there are three possible outcomes of the genetic analysis. In Figure 1, oocytes 1, 2, and 3 correspond to the three basic cases mentioned in the Chicago Tribune article. Starting with a primary oocyte from the affected woman prior to meiosis, based on your understanding of the events of meiosis, explain all three outcomes. For each case, state clearly the oocyte's and the polar body's genetic constitution during meiosis I and II. Use the diagram to explain your answer, drawing the chromosome(s) on which the APP gene resides. Feel free to use colored pens/pencils. Hint: case #3 is the most challenging (8 points) 4. Verlinsky and colleagues went on to perform the testing stated in Step 4 of the Chicago Tribune diagram, both to confirm the results of the first biopsy and to subsequently assess cases like those in Step 3c. Although not stated in the article, material with an undesirable genetic constitution is routinely discarded in these experiments. Your friend is a bioethicist, who is invited to give a talk to a group of pro-life university students holding a rally in Washington, DC at which President Bush will address the delegates. To your friend's surprise, some of the students cautiously approve of the use of Verlinsky and colleagues' technique. Using the Tribune diagram as a reference, which aspect(s) of the procedure would they find acceptable? State your reasoning clearly (6 points). Zoo 470 2008 Problem Set #1 Page 4 Medicine Before Conception CHICAGO, Feb. 27, 2002 In what is believed to be a medical first, a woman with a gene that is all but certain to cause Alzheimer's by her 40s gave birth to a baby free of the defect after having her eggs screened and selected in the laboratory. Experts said it appears to be the first time pre-implantation genetic diagnosis, or PGD, has been used for earlyonset Alzheimer's. There is no similar test for the more typical form of Alzheimer's, which strikes the elderly. PGD, which can also involve the testing of early embryos, has been used to screen for other devastating diseases such as Tay-Sachs and sickle-cell anemia, which strike in early childhood. It is less commonly used to detect diseases that strike adults. Medical ethicists say the latest milestone raises troubling issues, among them the rights of parents with disabling diseases to have children. The patient, a 33-year-old married geneticist who had the procedure about two years ago, desperately wanted children, even though Alzheimer's will probably steal her mind long before her daughter grows up. "Today it's early-onset Alzheimer's. Tomorrow it could easily be intelligence, or a good piano player or many other things we might be able to identify the genetic factors for," said Jeffrey Kahn, director of the University of Minnesota's Center for Bioethics. "The question is, whether we ought to." The patient, whose name was not released, has a brother and sister who developed Alzheimer's in their 30s. Tests showed that she has a mutation called V717L that has been found to lead to the formation of the brain-clogging protein deposits that are a hallmark of Alzheimer's. The woman was well-informed of the ramifications, said her doctor, geneticist Yury Verlinsky. A PGD pioneer at Chicago's Reproductive Genetics Institute, Verlinsky described his patient's procedure at a news conference Tuesday. A report on the case appears in Wednesday's Journal of the American Medical Association. The woman underwent in-vitro fertilization, in which eggs are fertilized in the lab and implanted in the womb. But first, the eggs were examined to find those that were free of the mutant gene. Her daughter was born about a year ago. The woman is pregnant again after undergoing another round of testing. Using PGD for early-onset Alzheimer's is "the only relief for at-risk couples," Verlinsky said. He said he will not screen for gender or other "cosmetic" reasons, but otherwise does not pass judgment on which patients he will test. "It's not our place to make a moral decision for them," he said. PGD is not widely available, partly because the defects it tests for are generally rare. It is also tricky to perform. Verlinsky said PGD procedures, developed in the late 1980s, have resulted in about 700 babies worldwide. His clinic has done about 2,000 PGD procedures, resulting in over 200 babies. PGD costs about $2,500 at Verlinsky's clinic. His patient had to undergo two rounds of tests because eggs tested the first time both had the V717L flaw. The cost does not include the clinic's $7,500 fee for in-vitro fertilization. The Alzheimer's-related flaw is probably present in only a dozen or so families worldwide, and afflicted patients are virtually assured of developing early-onset Alzheimer's, according to experts. Kahn said PGD is an unregulated, market-driven area of science, with some clinics already using the tests for gender selection and others willing to test for whatever is scientifically feasible. University of Pennsylvania bioethicist Arthur Caplan said such procedures are certain to prove highly controversial "because that's really getting into designing our descendants." "Testing for diseases that are going to appear 30 or 40 years from now, does that make any sense, since people are mortal?" Caplan asked. Testing for early-onset Alzheimer's falls within guidelines from the American Society of Reproductive Medicine, which sets standards for fertility clinics, said Andrea Bonnicksen, a member of the group's ethics committee. The group supports PGD when used for medical reasons, though clinics can decide for themselves which conditions to test for, she said. In a JAMA editorial, Dr. Dena Towner and bioethicist Roberta Springer-Loewy of the University of California at Davis said the Alzheimer's case raises troubling questions, since the woman "most likely will not be able to care for or even recognize her child in a few years." By Lindsey Tanner MMII The Associated Press. Zoo 470 2008 Problem Set #1 Page 5 Original paper: Verlinsky Y., Rechitsky S., Verlinsky O., Masciangelo C., Lederer K., and Kuliev A. (2002). Preimplantation diagnosis for early-onset Alzheimer disease caused by V717L mutation. Journal of the American Medical Association 287(8):1018-21. ...
View Full Document
This note was uploaded on 08/08/2008 for the course ZOO 470 taught by Professor Hardin during the Spring '08 term at Wisconsin.
- Spring '08