self-reps in CNS

self-reps in CNS - Self-Representation in Nervous Systems...

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DOI: 10.1126/science.1070564 , 308 (2002); 296 Science et al. Patricia S. Churchland, Self-Representation in Nervous Systems www.sciencemag.org (this information is current as of April 27, 2009 ): The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/296/5566/308 version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/cgi/content/full/296/5566/308#otherarticles , 3 of which can be accessed for free: cites 6 articles This article 30 article(s) on the ISI Web of Science. cited by This article has been http://www.sciencemag.org/cgi/content/full/296/5566/308#otherarticles 2 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/psychology Psychology : subject collections This article appears in the following http://www.sciencemag.org/about/permissions.dtl in whole or in part can be found at: this article permission to reproduce of this article or about obtaining reprints Information about obtaining registered trademark of AAAS. is a Science 2002 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the Science on April 27, 2009 www.sciencemag.org Downloaded from
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been noted by immunologists grappling with the origin of adaptive immunity ( 1 , 31 ), are a consequence of similar selective pressures for diversification and co-evolution of recognition functions to retain affinity between interaction partners. A hallmark of these specific recognition systems is that their genes are subject to intense diversifying selection. Large numbers of alleles are commonly found, and extraor- dinarily high levels of intraspecific polymor- phism are typically achieved, in some cases resulting from accelerated rates of evolution ( 18 , 32 ). Due to balancing selection, poly- morphisms in these genes can persist for long periods of time and often predate species diversification. Trans-species polymorphisms have been described in the MHC ( 33 ) and in SI systems ( 34 ), and in both cases, diver- gence of some allelic lineages appears to have occurred at least 20 million years ago. Another emerging commonality between recognition loci is their structural heteromor- phism, which apparently reduces intralocus recombination events and prevents disruption of the co-adapted gene complex. The crucifer S locus has been extensively restructured by expansion or contraction of the physical dis- tance between SRK and SCR , gene duplica- tion, as well as rearrangement of these two genes relative to each other and to flanking markers (Fig. 1) ( 18 , 35 ). Similarly, the MHC has undergone frequent gene duplications and deletions during its evolution ( 33 ), and the mating-type locus of Chlamydomonas con- tains a highly rearranged region that causes suppression of recombination over a 1-mega- base chromosomal region ( 36 ).
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