Re: Life explained

Rohinton Collins (
14 Nov 1996 00:41:42 GMT

> You quoted a good example:
> sickle cell anaemia. WHY has this not simply died out? (CLUES:
> admixture, diseases of the blood.)

Sickle Cell Anaemia is a genetic disease in which the gene responsible is
recessive with respect to its allele. If someone has only one copy of the
gene (termed a carrier) its phenotypic effect is actually beneficial. It
increases that person's resistance to malaria (by what degree, I am
unsure). This is how the gene has survived. When two carriers have
children, there will only be a 1 in 4 chance that their offspring will
inherit both genes and go on to develop the Sickle Cell disease. There is a
1 in 4 chance that the offspring will not have inherited the gene from
either parent. And a 1 in 2 chance that the offspring will have inherited
just one copy of the gene and will be itself, a carrier.

I hope that this has answered your question Mr Murray,