Julio knows that sickle cell disease is a serious genetic disorder. He learns that in the United States, approximately 1 in 12 people of African ancestry carries the sickle cell allele. He asks, "Why is the sickle cell allele present in such a high frequency?" Which statement would be MOST USEFUL to include in an answer to Julio's question?

A. The sickle cell allele causes a significant change to a blood protein.
B. The sickle cell allele formed from a point mutation.
C. Two copies of the sickle cell allele are necessary to express the disorder.
D. Having one copy of the sickle cell allele provides resistance to malaria.

The answer would be c, white eyes are homozygous recessive. in the early 1900s, morgan conducted several experiments with vinegar  flies (drosophila). one  sample revealed an anomaly: a  white-eyed, single male fly. he attempted to breed this fly with the typical red-eyed females. the offspring were all red-eyed. using flies from this new generation (brother-sister pairs)  produced some red-eyed and a few white-eyed flies. the white-eyed were all male. in later experiments, he was able to produce white-eyed females. this proved that white eyes are not lethal to either sex (ruling out a and b). since the percentage of white eyes to red eyes is so low, white eyes are not a dominant trait. it would be a recessive trait. 

Sorry  i don't understand can you rephrase that

Stimulates weight gain, so you put on excess weight