Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

21. Population Genetics

Allelic Frequency Changes

Genetics

21. Population Genetics

Allelic Frequency Changes

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2:48 minutes

Problem 4

Textbook Question

Describe how natural selection can produce balanced polymorphism of allele frequencies through selection that favors heterozygotes.

Verified step by step guidance

Understand the concept of balanced polymorphism, which occurs when two or more alleles are maintained in a population's gene pool at stable frequencies over time.

Recognize that heterozygote advantage (also called overdominance) is a form of natural selection where individuals with heterozygous genotypes have higher fitness than either homozygous genotype.

Set up the fitness values for the three genotypes: let the fitness of homozygote AA be

W_{AA}

, heterozygote Aa be

W_{Aa}

, and homozygote aa be

W_{aa}

, with

W_{Aa} > W_{AA}

and

W_{Aa} > W_{aa}

Use the concept that selection will increase the frequency of the heterozygote-favored allele combinations, but because both alleles contribute to heterozygotes, neither allele is lost, leading to a stable equilibrium of allele frequencies.

Explain that the equilibrium frequencies can be calculated by setting the change in allele frequency to zero and solving the equations derived from the relative fitness values, showing how natural selection maintains both alleles in the population.

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Key Concepts

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

Natural Selection

Natural selection is the process where individuals with traits better suited to their environment have higher survival and reproductive success. Over time, this leads to changes in allele frequencies within a population, favoring alleles that confer a fitness advantage.

Balanced Polymorphism

Balanced polymorphism occurs when two or more alleles are maintained in a population at stable frequencies due to selective advantages. This genetic diversity persists because heterozygotes have higher fitness than either homozygote, preventing any single allele from becoming fixed or lost.

Heterozygote Advantage

Heterozygote advantage is a form of selection where individuals with two different alleles (heterozygotes) have greater fitness than those with two identical alleles (homozygotes). This advantage maintains multiple alleles in the gene pool, as seen in cases like sickle cell trait providing malaria resistance.

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