2-1-11 Homologous Recombination II

2-1-11 Homologous Recombination II - Genetics in the News...

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1 Troubling times for embryo gene tests New Scientist 21 March 2006 Stu Hutson A number of distressing embryo-screening blunders highlight a lack of regulation in a fast-growing industry At the age of 4, Doreen Flynn's first daughter, Jordan, was diagnosed with Fanconi anemia , a rare genetic blood disorder that leaves people underweight and with a 700-fold greater chance of developing cancer. It is unlikely that Jordan will live past her early twenties. Flynn and her husband wanted to have more children, partly because a bone-marrow transplant from a healthy sibling would be Jordan's best shot at survival. They decided to undergo pre-implantation genetic diagnosis , an IVF technique designed to ensure only healthy embryos are implanted. A Detroit-based lab, Genesis Genetics Institute, isolated two apparently disease-free embryos that would be bone-marrow matches for Jordan and implanted them at a hospital in Atlanta in early 2003. Julia and Jorjia were born 34 weeks later. Both have Fanconi anemia. Genetics in the News (courtesy of Anna Dulencin) Review - Last group work : Can more than one pathway deal with thymine dimers? Photoreactivation (in organisms that have it) Nucleotide Excision Repair Base Excision Repair Translesion Synthesis Which pathways repair with high fidelity? Photoreactivation, NER, BER Which pathway does not? Translesion Synthesis February 1, 2011 Homologous Recombination, Part II Genetic Analysis 2 Robin Holliday's model was a conceptual breakthrough in several ways: • He understood that HR in meiosis must be initiated by DNA strand breaks . • The idea of strand exchange explained why and how HR was dependent upon sequence homology. • His model explained how the same process could give rise to either of two distinct outcomes: crossing over or gene conversion . See following figures (from Watson )… The Holliday Model for Homologous Recombination
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2 Later studies of recombination led to revisions of the Holliday model. In more recent models, the initiation of recombination happens differently: Two spontaneous nicks in the exactly the same location in two homologous DNA duplexes seemed unlikely. More probably, one DNA helix incurs a break in both strands . This was the basis of a model proposed in the 80’s by Jack Szostak, Terry Orr-Weaver, Rodney Rothstein and Frank Stahl; the “Double-Strand Break Repair ” (DSBR) model. The big innovation of the DSBR model was that it recognized that
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This note was uploaded on 04/04/2011 for the course GENETICS 385 taught by Professor Brennemanandgordon during the Spring '11 term at Rutgers.

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2-1-11 Homologous Recombination II - Genetics in the News...

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