--- Richard Baker <[EMAIL PROTECTED]> wrote: > Julia said: > > > OK, why *did* it survive? Do you know? > > I don't know about cystic fibrosis in detail, but > it's presumably > because having one copy of the gene conveys some > advantage that > outweighs the problems involved with having two > copies. Another example > is the incidence of thalassemia in Ferrara, Italy. > In that region, 18% > of people are born with one copy of the thalassemia > gene and 1% with > two copies. The unfortunate people with two copies > develop the disease, > and nearly all of them die young. However, until > WW2, Ferrara had been > afflicted with malaria for centuries, and the gene > for thalassemia > conveys resistance to malaria. About one in ten > people with no > thalassemia gene died of malaria whereas those with > one or two > thalassemia genes almost always survived. The > incidence of the gene was > thus kept at an equilibrium level: having the > occasional descendent who > dies of thalassemia is outweighed by having lots of > descendents who > don't die of malaria. > > Rich
Not sure if thalassemia is a European term for sickle cell anemia, which has the same effects. One copy of the cystic fibrosis gene conveys a high degree of resistance to cholera, so CF is prevalent in areas where there have been high historic rates of cholera infection. ===== Gautam Mukunda [EMAIL PROTECTED] "Freedom is not free" http://www.mukunda.blogspot.com __________________________________ Do you Yahoo!? Yahoo! Calendar - Free online calendar with sync to Outlook(TM). http://calendar.yahoo.com _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
