With Respect to the Sickle-Cell Allele, What Should Be True

Multiple Choice

With respect to the sickle-cell allele, what should be true of the β hemoglobin locus in U.S. populations of African-Americans whose ancestors were from equatorial Africa?
1) The average heterozygosity at this locus should be decreasing over time.
2) There is an increasing heterozygote advantage at this locus.
3) Diploidy is helping to preserve the sickle-cell allele at this locus.
4) Frequency-dependent selection is helping to preserve the sickle-cell allele at this locus.

A) 1 only
B) 1 and 3
C) 2 and 3
D) 1, 2, and 3
E) 1, 2, and 4