Which of the following statements about sickle cell disease is true?
it is caused by having 3 copies of chromosome 21.
it is a mild, painless illness that does not limit lifespan.
it primarily affects people of african descent.
it causes a person’s mucus to the excessively thick and sticky.

It primarily affects people of African descent.

In parts of Africa where malaria is common, a high per cent of the population

has the sickle cell trait. This is due to the fact that people with sickle cell trait are more resistant to malaria than others.

b) the heart is a pump made of muscle and that is difficult to grow in the lab.