Sickle Cell Anemia
& Natural Selection: Allison & Shannon :)
What is it exactly?
Sickle cells become "stuck" in the blood vessels blocking the flow of blood
As a result: Painful crisis in joints and bones etc.
The normal DNA sequence:
ATG GTG CAC CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT
Sickle Cell DNA Sequence:
ATG GTG CAC CTG ACT CCT GTG GAG AAG TCT GCC GTT ACT
**Valine is switched in the DNA sequence for glutamic acid
How is this an example of Natural Selection?
This is an example of the Mendel Principle: Incomplete dominance
•One allele is not completely dominant over another
The AS carriers are more likely to survive because:
• Not susceptible to Malaria
•AS and AS equal 25% SS and 50% AS
The SS are less likely to survive because:
• Highly susceptible to Malaria
•SS and AS equal 50% SS and 50% AS
**If more people have the AS trait rather than the SS, then the carrier (AS) trait means a higher chance of survival.
AA : Normal
SS : Sickle Cell Anemia
AS : Carrier
•A and S are Co Dominant
How the protein changes/mutates from Glutamic acid to Valine (GAG to GUG)
In the case of AS & AS
[50% AS] [25% SS] [25% AA]
Formation of sickled cells
The sickling of a red blood cell
What does it look like?
How Likely Is This?
1 in 500 develop Sickle Cell Anemia in the U.S.
1 in 100 develop Sickle Cell Anemia in Africa
Why is the risk higher in Africa?
•Malaria more common from mosquitoes