First of all I would like to explain both of the diseases so we can get the relation well...:)

Sickle Cell Anemia:

The sickle cell mutation is a like a typographical error in the DNA code of the gene that tells the body how to make a form of hemoglobin (Hb), the oxygen-carrying molecule in our blood. Every person has two copies of the hemoglobin gene. Usually, both genes make a normal hemoglobin protein. When someone inherits two mutant copies of the hemoglobin gene, the abnormal form of the hemoglobin protein causes the red blood cells to lose oxygen and warp into a sickle shape during periods of high activity. These sickled cells become stuck in small blood vessels, causing a "crisis" of pain, fever, swelling, and tissue damage that can lead to death. This is sickle cell anemia.


Malaria:

Malaria is a potentially fatal blood disease caused by a parasite that is transmitted to human and animal hosts by the Anopheles mosquito. The human parasite, Plasmodium falciparum, is dangerous not only be cause it digests the red blood cell's hemoglobin, but also because it changes the adhesive properties of the cell it inhabits. This change in turn causes the cell to stick to the walls of blood vessels. It becomes especially dangerous when the infected blood cells stick to the capillaries in the brain, obstructing blood flow, a condition called cerebral malaria. Scientists using the x-ray microscope are hoping to learn more about the how the parasite infects and disrupts the blood cells and the blood vessels of an infected host.

So these diseases have a special relationship between them. They don't actually 'cause' each other but if a person's cells inherit a sickle cell gene this makes him resistant for the malaria disease ;it is an advantageous position. So the relation between sickle cell anemia and malaria is an example of correlation without causation. One copy of the gene is beneficial. If a person has one copy of the gene their offspring has a %50 chance of receiving a one copy of the gene and become lucky.However these carriers are naturally selected. 


Work Cited


http://www.buzzle.com/articles/sickle-cell-and-malaria.html.Web.Feb 12,2012
http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html. Web. Feb 12,2012
http://www.lbl.gov/MicroWorlds/xfiles/malariawhatis.html Web. Feb 12, 2012