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Ch. 26 - Population and Evolutionary Genetics
Chapter 25, Problem 21

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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span>Step 1: Understand the problem. We have a population of 50 desert bighorn sheep. The allele c is recessive and causes curled coats when homozygous (cc). The allele C is dominant and results in straight coats. We need to find the inbreeding coefficient F.</span
span>Step 2: Identify the given data. We know there are 4 sheep with curled coats (cc), and 17 sheep are heterozygous carriers (Cc). The total population is 50 sheep.</span
span>Step 3: Calculate the observed frequency of the homozygous recessive genotype (cc). This is the number of sheep with curled coats divided by the total population: \( f(cc) = \frac{4}{50} \).</span
span>Step 4: Calculate the observed frequency of the heterozygous genotype (Cc). This is the number of heterozygous carriers divided by the total population: \( f(Cc) = \frac{17}{50} \).</span
span>Step 5: Use the Hardy-Weinberg principle to estimate the expected frequencies of the genotypes under random mating, and then use these to calculate the inbreeding coefficient F, which measures the reduction in heterozygosity due to inbreeding.</span

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Key Concepts

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

Inbreeding Coefficient (F)

The inbreeding coefficient (F) quantifies the probability that two alleles at a locus in an individual are identical by descent. It ranges from 0 (no inbreeding) to 1 (complete inbreeding). Inbreeding can lead to an increase in homozygosity and can affect the genetic health of a population, making it crucial for understanding genetic diversity and potential vulnerabilities.
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Allele Frequencies

Allele frequency refers to how often a particular allele appears in a population's gene pool. It is calculated by dividing the number of copies of the allele by the total number of alleles for that gene in the population. Understanding allele frequencies is essential for calculating the inbreeding coefficient and assessing genetic variation within a population.
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Heterozygosity

Heterozygosity is the presence of different alleles at a gene locus in an individual. It is an important measure of genetic diversity within a population. High levels of heterozygosity are generally associated with greater adaptability and resilience to environmental changes, while low heterozygosity can indicate inbreeding and reduced genetic health.
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Related Practice
Textbook Question

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

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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

To increase genetic diversity in the bighorn sheep population described in Problem 23, ten sheep are introduced from a population where the c allele is absent. Assuming that random mating occurs between the original and the introduced sheep, and that the c allele is selectively neutral, what will be the frequency of c in the next generation?

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Textbook Question

What genetic changes take place during speciation?

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Textbook Question

Some critics have warned that the use of gene therapy to correct genetic disorders will affect the course of human evolution. Evaluate this criticism in light of what you know about population genetics and evolution, distinguishing between somatic gene therapy and germ-line gene therapy.

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