C.only determines phenotype when a dominant allele for the same trait is present.
Answer:
Differential reproduction leads to a change in allele frequencies over time. This occurs because of natural selection favoring "successful" individuals that produce more viable offspring.
The sickle-cell allele is maintained in populations exposed to malaria through balancing selection, since heterozygous individuals have protection against the disease.
Answer:
Gravity draws the matter in an interstellar cloud together to form a star.
