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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Multiple Choice

Which evolutionary process best explains the high frequency of the HbS allele in regions of Africa where malaria is endemic?

Gene flow from non-African populations

Genetic drift due to small population size

Mutation introducing new HbS alleles at a high rate

Natural selection favoring heterozygotes for resistance to malaria

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Verified step by step guidance

Understand the context: The HbS allele is a variant of the hemoglobin gene that provides resistance to malaria when present in a heterozygous state (one copy of HbS and one normal allele). This is a classic example of a balanced polymorphism.

Recall the evolutionary processes: Gene flow involves movement of alleles between populations, genetic drift is random change in allele frequencies often in small populations, mutation introduces new alleles but usually at a low rate, and natural selection favors alleles that increase fitness in a given environment.

Analyze the environment: In regions where malaria is endemic, individuals with one copy of the HbS allele (heterozygotes) have a survival advantage because they are more resistant to malaria, while homozygotes for HbS suffer from sickle cell disease.

Apply the concept of heterozygote advantage (overdominance): Natural selection maintains the HbS allele at a high frequency because heterozygotes have higher fitness than either homozygote, leading to balanced polymorphism in the population.

Conclude that natural selection favoring heterozygotes best explains the high frequency of the HbS allele in malaria-endemic regions, rather than gene flow, genetic drift, or mutation.