tag:blogger.com,1999:blog-8480427453110572235.post1956809254673645409..comments2008-03-19T17:45:32.004+11:00Danielhttp://www.blogger.com/profile/07276690118219000204noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-8480427453110572235.post-58414693431775482642008-03-19T17:45:00.000+11:002008-03-19T17:45:00.000+11:00<I>Disease susceptibility genes can be maintained in the population in a number of ways.</I><BR/><BR/>Disease susceptability genes and disease CAUSING genes are two completely different things. <BR/><BR/>Just because a gene might increase the odds that someone will catch the flu (or any common illness) doesn't mean that the flu is spread through genes. Most of the "disease" genes that end up in stories in the major media are perfectly healthy. The overwhelming majority of fitness reducing condition are the result of negative, environmental input like pathogens, pollution, poor nutrition, injury, etc. <BR/><BR/>I know you're smart, but since it's election season I'll use this line.<BR/><BR/>It's the environment stupid. 8-)germ-o-phobehttp://www.blogger.com/profile/07630125480792322730noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-59930057467403346282008-03-16T16:43:00.000+11:002008-03-16T16:43:00.000+11:00<I>If heritable genes caused common illnesses in humans this might be a significant problem. But they don't.</I><BR/><BR/>Yes, they do. Most common diseases have a substantial heritable component, and the individual genes responsible are slowly being identified. As just a single example, the <A HREF="http://www.nature.com/nature/journal/v447/n7145/abs/nature05911.html" REL="nofollow">WTCCC genome-wide scans</A> identified 24 genetic variants that are associated with one or more of seven different common diseases (ranging from bipolar disease to type 2 diabetes).<BR/><BR/><I>Any common gene that leads to increased susceptability to problem X also offers increased immunity to problem Z. Environmental damage/input is always required. Mathematically it can't work any other way. If it wasn't a game of pluses and minuses these susceptability genes would get obliterated in short order.</I><BR/><BR/>Disease susceptibility genes can be maintained in the population in a number of ways. You've already noted one, which is when disease variants also provide protection from some environmental condition - for instance, <A HREF="http://www.genetic-future.com/2008/02/why-do-we-have-common-risk-variants-for.html" REL="nofollow">metabolic disease genes may be involved in adaptation to novel environments</A>. Other mechanisms include <A HREF="http://www.genetic-future.com/2008/03/climate-genes-positive-or-balancing.html" REL="nofollow">heterozygote advantage</A>, when a variant provides an advantage when it is present as one copy but causes disease when present as two copies. Disease variants can also simply slip through the cracks and drift to high frequency even when they are moderately deleterious, especially during a population bottleneck followed by an expansion (as likely occurred for most groups of modern humans).<BR/><BR/>The take-home message: common disease variants certainly do exist, and have reached moderate frequency in the human population via multiple known mechanisms; and population genetics is not as simple as you seem to think it is.Danielhttp://www.blogger.com/profile/07276690118219000204noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-76762599843322802762008-03-15T03:22:00.000+11:002008-03-15T03:22:00.000+11:00If heritable genes caused common illnesses in humans this might be a significant problem. But they don't.<BR/><BR/>Any common gene that leads to increased susceptability to problem X also offers increased immunity to problem Z. Environmental damage/input is always required. Mathematically it can't work any other way. If it wasn't a game of pluses and minuses these susceptability genes would get obliterated in short order.<BR/><BR/>Rare disorders are a different story. It's too bad that phenomenon like Founder Effect can keep bad mutations around longer than they would otherwise last in nature.germ-o-phobehttp://www.blogger.com/profile/07630125480792322730noreply@blogger.comtag:blogger.com,1999:blog-8480427453110572235.post-78267178614772952582008-02-27T03:26:00.000+11:002008-02-27T03:26:00.000+11:00Hi Daniel,<BR/><BR/>I've been following your blog via the DNA Network, and I think you write great stuff. What would you think about being a writer on <A HREF="http://www.scientificblogging.com" REL="nofollow">Scientific Blogging</A>? It doesn't mean that you would move this blog, but you'd have a chance to write for a broad non-expert audience - we got 600,000 visitors in January. We're looking for more people of your caliber.<BR/><BR/>I'm a postdoc at Washington University's Center for Genome Sciences, and I write the blog <A HREF="http://adaptivecomplexity.blogspot.com" REL="nofollow">Adaptive Complexity</A>. If you're interested in more info about Scientific Blogging, send me an email at mwhite@genetics.wustl.edu. Sorry to solicit this on your blog, but I couldn't find your email on your research group's website.<BR/><BR/>MikeMikehttp://www.blogger.com/profile/00474549004146223010noreply@blogger.com