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

Question

Quizplus · Accepted Answer

The β hemoglobin locus in U.S. populations of African-Americans whose ancestors were from equatorial Africa should have a high frequency of the sickle-cell allele due to historical natural selection. This means that there is likely a high level of heterozygosity at this locus, as carriers of the sickle-cell allele are relatively protected against malaria. However, over time, as malaria becomes less prevalent in these populations, the heterozygosity at this locus should decrease (choice 1). Diploidy (choice 3) is not directly related to the preservation of the sickle-cell allele, but rather a general genetic mechanism for preserving genetic diversity. Frequency-dependent selection (choice 4) may also help to maintain the sickle-cell allele in some populations, but this is not a major factor in U.S. populations of African-Americans. Therefore, the best choice is B (1 and 3).

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