tag:blogger.com,1999:blog-8480427453110572235.post6105722276942168311..comments2008-04-23T09:16:09.769+10:00Danielhttp://www.blogger.com/profile/07276690118219000204noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-8480427453110572235.post-52346080630083897492008-04-23T09:16:00.000+10:002008-04-23T09:16:00.000+10:00Hi Valeria,<BR/><BR/>Yes, I think spatially varying selection absolutely qualifies as a form of balancing selection. As I mentioned to razib above, I didn't discuss this possibility as I wasn't able to find much information on the specific requirements (levels of gene flow, strength of selection) for this type of balancing selection to operate, so I'm unsure how realistic it is for the human population. Razib has referred me to a book chapter that might help once I track it down.<BR/><BR/>If this is in fact the type of balancing selection that is operating, then my entire post is basically an exercise in semantics - the authors were totally correct when they talked about "spatially varying positive selection", and I'm also correct when I refer to it as "balancing selection"!Danielhttp://www.blogger.com/profile/07276690118219000204noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-4822073008360059632008-04-23T04:34:00.000+10:002008-04-23T04:34:00.000+10:00I liked your post a lot and I find your hypothesis more than convincing...<BR/>I'm struggling with clines and selection my self and I would like to ask you a question, which is merely about definitions and terminology: do you think that spatially varying positive selection can be defined as balancing selection, if you take into account the whole population, from North to South? From this point of view the system is maintaining different alleles which are better adapted to different environments, which is exactly what balancing selection is supposed to do. <BR/>Thanks a lot!Valeriahttp://www.blogger.com/profile/08699114205381727471noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-80235896083586280602008-03-11T17:21:00.000+11:002008-03-11T17:21:00.000+11:00check out the chapter's in <I>genetics of populations</I> by hedrick.Razibhttp://www.blogger.com/profile/09555115542918519593noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-56617000229014039792008-03-11T02:02:00.000+11:002008-03-11T02:02:00.000+11:00Heh, I'm currently struggling through the literature on precisely that issue. I left it out of the post (and used the weasel word "classically") because fluctuating selection is a much more contentious mechanism than overdominance or frequency-dependent selection. However, I'm trying to get to grips with it because it seems like it might be highly relevant to climate adaptation.<BR/><BR/>The literature is actually surprisingly scarce on this issue, possibly because the added variables (the temporal and spatial scale of variation) make it tough to model. Hopefully I'll be knowledgeable enough to post on it over the next couple of weeks.Danielhttp://www.blogger.com/profile/07276690118219000204noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-67780794819645758282008-03-10T17:38:00.000+11:002008-03-10T17:38:00.000+11:00<I>Balancing selection is a special case of selection, which results in multiple versions of the same gene all being maintained at some frequency within the population, sometimes over a very long period of time. Classically, balancing selection occurs in two situations:</I><BR/><BR/>i was taught that environmental & temporal heterogeneity could also do the trick.Razibhttp://www.blogger.com/profile/09555115542918519593noreply@blogger.com