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Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 20, Problem 13a

Two populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland. If you compared the allele frequencies in the two populations, what would you expect to find?

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1
Understand the concept of gene flow: Gene flow refers to the transfer of alleles or genes from one population to another. In this case, migration across the land bridge facilitates gene flow between the mainland and island deer populations.
Consider the size of the populations: The mainland population is large, while the island population is small. This difference in population size affects the impact of gene flow. Allele frequencies in the smaller island population are more likely to be influenced by incoming migrants from the mainland.
Analyze the effect of migration: Migration tends to homogenize allele frequencies between populations. Over time, the allele frequencies in the island and mainland populations will become more similar due to the regular exchange of individuals.
Account for genetic drift: In the smaller island population, genetic drift (random changes in allele frequencies) may have a stronger effect compared to the larger mainland population. However, gene flow from the mainland can counteract these random changes, stabilizing allele frequencies.
Predict the outcome: Given regular migration, you would expect the allele frequencies in the two populations to converge over time, becoming more similar. However, the rate of convergence depends on the migration rate and the relative sizes of the populations.

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Key Concepts

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

Allele Frequency

Allele frequency refers to how often a particular allele appears in a population compared to other alleles for the same gene. It is a key measure in population genetics, indicating genetic diversity and the potential for evolution. Changes in allele frequencies over time can signal evolutionary processes such as natural selection, genetic drift, or gene flow.
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New Alleles and Migration

Gene Flow

Gene flow is the transfer of genetic material between populations through migration and interbreeding. In the context of the deer populations, the exchange of members across the land bridge allows for gene flow, which can alter allele frequencies by introducing new alleles or changing the proportions of existing ones. This process can reduce genetic differences between populations and increase genetic diversity.
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Population Structure

Population structure refers to the composition of a population in terms of genetic variation and how it is distributed among subpopulations. In this scenario, the mainland and island deer populations may exhibit different allele frequencies due to their distinct environments and sizes. However, regular migration can lead to homogenization of allele frequencies, making the populations more genetically similar over time.
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Related Practice
Textbook Question

A 9-bp deletion in the mitochondrial genome between the gene for cytochrome oxidase subunit II and the gene for tRNAᴸʸˢ is a common polymorphism among Polynesians and also in a population of Taiwanese natives. The frequency of the polymorphism varies between populations: The highest frequency is seen in the Maoris of New Zealand (98%), lower levels are seen in eastern Polynesia (80%) and western Polynesia (89%), and the lowest level is seen in the Taiwanese population. What do these frequencies tell us about the settlement of the Pacific by the ancestors of the present-day Polynesians?

Textbook Question

When the human genome is examined, the chromosomes appear to have undergone only minimal rearrangement in the 100 million years since the last common ancestor of eutherian mammals. However, when individual humans are examined or when the human genome is compared with that of chimpanzees, a large number of small indels and SNPs can be detected. How are these observations reconciled?

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Textbook Question

Look over the 10 diseases approved for genetic health risk assessment listed in Application Chapter B. Select one disease other than the three discussed in Application Chapter B or in this chapter (alpha-1 antitrypsin deficiency, late-onset Alzheimer disease, and celiac disease) or another of the diseases of your choice. Do a brief Internet search to find and download (1) one article for a nonscientific audience identifying the gene or genes whose alleles are associated with occurrence of the disease and (2) one scientific paper that provides data supporting the association of specific alleles of the gene or genes with the disease. Write a short summary combining the information contained in the two papers.

Textbook Question

Two populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland. An earthquake destroys the bridge between the island and the mainland, making migration impossible for the deer. What do you expect will happen to allele frequencies in the two populations over the following 10 generations?

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Textbook Question

Two populations of deer, one of them large and living in a mainland forest and the other small and inhabiting a forest on an island, regularly exchange members that migrate across a land bridge that connects the island to the mainland. In which population do you expect to see the greatest allele frequency change? Why?

Textbook Question
Directional selection presents an apparent paradox. By favoring one allele and disfavoring others, directional selection can lead to fixation (a frequency of 1.0) of the favored allele, after which there is no genetic variation at the locus, and its evolution stops. Explain why directional selection no longer operates in populations after the favored allele reaches fixation.