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Sickle Cell Inheritance
Exploring Genetics and Probability
What is sickle cell?
• Sickle cell is a genetic condition that causes
the red protein in blood (hemoglobin) to make
the blood cells rigid and pointy.
• The gene for sickle trait is spread throughout
the world.
• It was most common in the areas where there
was a lot of malaria because sickle trait
actually helps people survive malaria.
What is sickle trait?
• In order to inherit anything from your parents,
you get one gene from each parent.
• The way sickle cell disease occurs is if you get
a sickle gene from both your parents.
• If you only get one sickle gene and your other
gene is normal, you have sickle trait.
Health Benefit of Sickle Trait
• Protects against risk of death from malaria
infection.
– Malaria kills thousands of kids a year.
• Note: only sickle trait gives protection against
the deadly strains of malaria
More on Malaria
• Caused by a parasite that can live in
mosquitoes
• Parasites infect red blood cells
• Symptoms include fever, vomiting, headache
• Can cut off blood supply to vital organs
• Different strains of malaria, some are deadly
• Children are very susceptible to dying of
malaria
Myth vs Reality
• Myth: Only African Americans get sickle cell.
• Reality: Sickle cell affects people of all
different racial and ethnic backgrounds.
– African, Arabian, Israeli, Turkish, Pakistani
– Greek, Hispanic, Italian
– Blond hair/blue eyed children of Northern Europe
– One case in Hong Kong!
Where do people have sickle cell?
• Highest frequency in Sub-Saharan Africa
• Also prevalent across the US, on the Atlantic
side of Central and South America, the
Caribbean, Europe, North and Central Africa,
the Middle East and South Asia.
Map from Dr. Lewis Hsu, MD, PhD
Professor of Pediatrics,
Director of Pediatric Sickle Cell,
University of Illinois, Chicago, IL
Inheriting a sickle gene
This is a genetic condition, so whether
somebody gets sickle cell disease or sickle trait
depends completely on what genes you get
from your parents.
The Inheritance Game
A S – Sickle trait
S S – Sickle Cell Disease
A A – Normal
Modeling inheritance
Mother’s genes
A
A
AA
Father’s
genes
S AS
Normal
Sickle
trait
Sickle trait
S
AS
Sickle trait
SS
Sickle cell disease
Sickle trait
Acknowledgements
• Adapted from ideas by
– Camille Coleman, Genetic Counselor, Marian
Anderson Comprehensive Sickle Cell Center,
St. Christopher’s Hospital for Children,
Philadelphia, PA
– Lewis Hsu, MD, PhD, Professor of Pediatrics,
Director of Pediatric Sickle Cell,
University of Illinois, Chicago, IL
– Rebecca Hui, 4th Grade Teacher,
St. Frances of Rome School, Chicago, IL
References and Related Resources
• Center for Disease Control
• Sickle Cell Information Center