Multiple Choice
The number of individuals in a population with each of the following genotypes is listed below. What is the frequency of the small t allele?
TT: 640
Tt: 200
tt: 160
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22. Evolution of Populations
Genetics and Allele Frequencies
Multiple Choice
How does the recessive sickle-cell allele remain in the gene pool despite its negative effects?
A
It provides a survival advantage in malaria-endemic regions.
B
It is always expressed in individuals, leading to natural selection.
C
It is eliminated from the population through genetic drift.
D
It is frequently mutated back into a dominant allele.
Verified step by step guidance1
Understand the concept of a recessive allele: A recessive allele is one that is expressed in the phenotype only when two copies are present (homozygous recessive). In the case of sickle-cell anemia, individuals with two copies of the sickle-cell allele (HbS) exhibit the disease.
Recognize the concept of heterozygote advantage: In malaria-endemic regions, individuals who are heterozygous (carriers) for the sickle-cell allele (HbA/HbS) have a survival advantage because they are less susceptible to malaria compared to individuals with two normal alleles (HbA/HbA).
Analyze the role of natural selection: The heterozygote advantage means that carriers of the sickle-cell allele have a higher chance of surviving and reproducing in malaria-endemic areas, thus passing on the allele to the next generation.
Consider the impact of genetic drift: While genetic drift can lead to the random loss of alleles in small populations, the sickle-cell allele persists in larger populations due to the selective advantage it provides in certain environments.
Evaluate the mutation rate: Although mutations can occur, the sickle-cell allele is not frequently mutated back into a dominant allele. The persistence of the allele is primarily due to the selective advantage in malaria-endemic regions, not frequent mutation.
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