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Ch. 26 - Population and Evolutionary Genetics
Chapter 25, Problem 18

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

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Consider the role of mutation: Mutations introduce new genetic variations into a population by altering DNA sequences. These changes can be beneficial, neutral, or deleterious, and they contribute to the genetic diversity within a population.
Examine the impact of gene flow: Gene flow, or the movement of genes between populations, can introduce new alleles into a population, increasing genetic variation. This occurs when individuals from different populations interbreed.
Analyze the effects of natural selection: Natural selection can maintain genetic variation by favoring different alleles in different environments or by balancing selection, where multiple alleles are maintained in a population due to selective advantages.
Consider genetic drift: Genetic drift is the random fluctuation of allele frequencies in a population. In small populations, genetic drift can lead to significant changes in allele frequencies, contributing to genetic variation.
Explore the role of sexual reproduction: Sexual reproduction increases genetic variation by combining alleles from two parents to produce offspring with unique genetic combinations. This recombination of alleles during meiosis and fertilization contributes to the genetic diversity of a population.

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Key Concepts

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

Genetic Variation

Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation is crucial for evolution and adaptation, as it provides the raw material for natural selection to act upon. High levels of genetic variation can enhance a population's ability to survive environmental changes and resist diseases.
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Natural Selection

Natural selection is a process where individuals with advantageous traits are more likely to survive and reproduce, passing those traits to the next generation. This mechanism can influence genetic variation by favoring certain alleles over others, but it can also maintain variation if different traits confer advantages in varying environments, leading to a balance of traits within a population.
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Gene Flow

Gene flow, or gene migration, is the transfer of genetic material between populations through processes such as migration and interbreeding. This exchange can introduce new alleles into a population, increasing genetic diversity and counteracting the effects of genetic drift, which can reduce variation. Gene flow is essential for maintaining genetic variation, especially in fragmented habitats.
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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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