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Ch. 26 - Population and Evolutionary Genetics
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 26, Problem 18

What are considered significant factors in maintaining the surprisingly high levels of genetic variation in natural populations?

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1
Understand that genetic variation in natural populations is influenced by multiple evolutionary and ecological factors that maintain diversity over time.
Consider the role of mutation as a source of new genetic variants, introducing new alleles into the population's gene pool.
Examine how natural selection, particularly balancing selection (such as heterozygote advantage or frequency-dependent selection), can maintain multiple alleles at a locus.
Analyze the impact of gene flow (migration) between populations, which can introduce new alleles and prevent populations from becoming genetically uniform.
Recognize the importance of population size and genetic drift, where large populations tend to maintain more variation, and mechanisms like recombination during sexual reproduction also contribute to genetic diversity.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Genetic Drift and Population Size

Genetic drift refers to random changes in allele frequencies, which can reduce genetic variation, especially in small populations. However, large population sizes help maintain variation by minimizing the impact of drift, allowing more alleles to persist over time.
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Mutation as a Source of Variation

Mutations introduce new genetic variants into a population by altering DNA sequences. Although most mutations are neutral or harmful, some can increase genetic diversity and provide raw material for evolution, helping maintain variation in natural populations.
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Balancing Selection and Heterozygote Advantage

Balancing selection maintains multiple alleles in a population by favoring genetic diversity. One example is heterozygote advantage, where individuals with two different alleles have higher fitness than homozygotes, preserving variation at specific loci.
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Related Practice
Textbook Question

Describe how populations with substantial genetic differences can form. What is the role of natural selection?

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Textbook Question

Achondroplasia is a dominant trait that causes a characteristic form of dwarfism. In a survey of 50,000 births, five infants with achondroplasia were identified. Three of the affected infants had affected parents, while two had normal parents. Calculate the mutation rate for achondroplasia and express the rate as the number of mutant genes per given number of gametes.

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Textbook Question

A recent study examining the mutation rates of 5669 mammalian genes (17,208 sequences) indicates that, contrary to popular belief, mutation rates among lineages with vastly different generation lengths and physiological attributes are remarkably constant [Kumar, S., and Subramanian, S. (2002). Proc. Natl. Acad. Sci. USA 99:803–808]. The average rate is estimated at 12.2×10⁻⁹ per bp per year. What is the significance of this finding in terms of mammalian evolution?

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Textbook Question

A botanist studying water lilies in an isolated pond observed three leaf shapes in the population: round, arrowhead, and scalloped. Marker analysis of DNA from 125 individuals showed the round-leaf plants to be homozygous for allele r1, while the plants with arrowhead leaves were homozygous for a different allele at the same locus, r2. Plants with scalloped leaves showed DNA profiles with both the r1 and r2 alleles. Frequency of the r1 allele was estimated at 0.81. If the botanist counted 20 plants with scalloped leaves in the pond, what is the inbreeding coefficient F for this population?

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Textbook Question

A farmer plants transgenic Bt corn that is genetically modified to produce its own insecticide. Of the corn borer larvae feeding on these Bt crop plants, only 10 percent survive unless they have at least one copy of the dominant resistance allele B that confers resistance to the Bt insecticide. When the farmer first plants Bt corn, the frequency of the B resistance allele in the corn borer population is 0.02. What will be the frequency of the resistance allele after one generation of corn borers have fed on Bt corn?

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Textbook Question

In an isolated population of 50 desert bighorn sheep, a mutant recessive allele c when homozygous causes curled coats in both males and females. The normal dominant allele C produces straight coats. A biologist studying these sheep counts four with curled coats. She also takes blood samples from the population for DNA analysis, which reveals that 17 of the sheep are heterozygous carriers of the c allele. What is the inbreeding coefficient F for this population?

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