Sickle Cell Anemia

Inheritance	autosomal recessive
Occurrence	1 in 375 African Americans have the disease and 1 in 10 are carriers.
Description	disease causing the red blood cells in the body to have a sickle shape (not a round shape). These sickle shapes can block veins, arteries, and capillaries and cause blood flow to an area to be stopped for a while. This can have serious side effects such as tissue death and stroke.
Testing for sickle cell disease	is available to individuals through a blood sample-- the test can identify both homozygous and heterozygous individuals. There is also a prenatal test.

One is great-- Two is not

Sickle cell anemia can be used and discussed during many biology units: first, when studying Mendelian traits directly, second when studying red blood cells, third when studying evolutionary mechanisms, and fourth when studying diseases transmitted by insects (Malaria). The activity below fits in best with evolutionary mechanisms but can be adapted easily.

Divide the class into four groups. It may help to have identification tags for them to wear. These are the titles of the four groups.

(4) Individuals who are not affected nor are they carriers of sickle cell disease

Have the mosquitoes move around the room until they transmit Malaria to everyone. They can put red stickers on those who have malaria. Allow this to continue for a few minutes. Have the students return to their desks. Have everyone stand up except the mosquitoes. Inform the individuals who have sickle cell disease, that they died from the disease and have them sit down. Inform the individuals who are not carriers and do not have sickle cell disease, that they have died from Malaria and have them sit down. Only carriers for sickle cell should be standing.ls who are carriers stand up. Inform them that they are lucky. Being a carrier for sickle cell disease provided a defense against Malaria and since they do not have sickle cell anemia, they are still alive.

The carriers' genotype is Aa. Since only carriers are left to reproduce, what genotypes and phenotypes of children will they have? Can the class see how natural selection is working to select carriers? Can the class see the double-edged sword-- that one copy of the gene is a great benefit whereas two copies of the gene causes a deadly disease? This type of selection is called balancing selection.