Figure 151 Shows the Three Alleles for the Beta-Globin Gene

Figure 15.1 shows the three alleles for the beta-globin gene. Which of the following statements BEST describes the effect of having the S allele, which codes for sickle-cell anemia?

A) Having the allele is always harmful.
B) Having the allele is always beneficial.
C) The effect depends on whether the allele occurs in its homozygous or heterozygous form.
D) The effect depends on the environment (i.e., whether malaria is present) .
E) The effect depends on whether the allele occurs in its homozygous or heterozygous form, and the environment (i.e., whether malaria is present) .