Question

Sickle-cell disease is caused by a mutation that produces an abnormal protein. The gene for sickle-cell disease causes a person's red blood cells to be shaped like a sickle instead of being round and flat. Sickle-shaped red blood cells do not carry oxygen very well, which causes health problems and lowers survival rate. However, in areas where malaria is common, people that have the sickle-cell gene are protected from malaria. The malaria parasite relies on normal red blood cells to grow, and cannot easily complete its life cycle in sickle-shaped cells.

What does the given information demonstrate?
A.
All mutations in humans result in a neutral effect.
B.
A mutation's negative effects always outweigh its benefits.
C.
All mutations always have both good and bad effects.
D.
A mutation can be both harmful and beneficial.

Answer 1

D. A mutation can be both harmful and beneficial.

Explanation: The sickle-cell mutation causes harmful effects (poor oxygen transport, health problems) but also provides protection against malaria in regions where malaria is common — showing a single mutation can have both negative and positive effects (heterozygote advantage).