Sickle Cell Anemia

& Natural Selection: Allison & Shannon :)

What is it exactly?

Caused by a mutation in the hemoglobin gene

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?

Natural Selection: Having certain genotypic characteristics better developed to an environment and survival


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

Big image

What does it look like?

Blood Cells

Hemoglobin forms long, inflexible chains rather than circular groups
Big image

How Likely Is This?

2.5 Million African Americans are carriers (AS)


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