G'day Mark,
I remember hearing about this during my undergrad. It was pertaining
to one of the coastal countries in africa (I think). What they found was that
there was a high incidence of sickle cell anaemia in the region. It was pondered
why it should have such a high incidence when it was on a recessive allele and
the condition was life threatening. It was also seen that there was a low
incidence of malaria.
What was happening was that there was a positive selection for ppl that
were carriers (ie. heterologous). As they only carried one copy of the gene, it
wasn't a life threatening condition, but there were sufficient sickle cells to
prevent infection by malaria (can't remember if the mechanism was to do with the
mosquito having trouble taking up the blood or the plasmodium).
Those that didn't carry the gene were more susceptible to malaria and
those that carried two copies of the gene suffered from sickle cell anaemia.
Anyway hope that helped,
Alistair
