Biology- Sickle Cell Anemia (SCA)

Question 1

Sickle Cell Anemia

Answer 1

SCA is due to a mutation in gene for hemoglobin (oxygen carrier in red blood cells) – require 2 copies of SCA allele to have disease – causes anemia (low rbc), organ damage, joint pain, and strokes

Question 2

What happens to the red blood cells in SCA?

Answer 2

rbc become stiff, sticky and crescent shaped and then block blood vessels

Question 3

HETEROZYGOUS ADVANTAGE –

Answer 3

heterozygote has a greater chance of survival and reproduction than either homozygote (e.g. normal or SCA)
Best example is SCA

Question 4

Where does SCA pose as an advantage?

Answer 4

Advantage is only found in areas of world where malaria is prevalent, mainly tropical and sub-tropical regions (parts of Africa, Central and South America, and Caribbean, India)

Question 5

Heterozygotes (sickle cell trait) –

Answer 5

resistant to malaria (deadly mosquito-carried parasite) as they have some sickled rbc (poor home for parasite)

Question 6

Homozygous SCA –

Answer 6

survive malaria, but die prematurely due to SCA

Question 7

Homozygous normal –

Answer 7

higher risk of death due to malaria, all normal rbc (host to malaria parasite)

Question 8

Remember**

Answer 8

Because of higher survival rate of heterozygotes in malaria-prone regions, they have a greater chance of reproducing, thus passing the SCA allele on to the next generation  results in higher incidence of allele in people from these regions (and their ancestors)
Maintains a “harmful” allele at otherwise unexpectedly high levels (e.g. allele is an adaptation in certain environments)