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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
21. Population Genetics
Hardy Weinberg
Problem 25a
Textbook Question
In a population of flowers growing in a meadow, C1 and C2 are autosomal codominant alleles that control flower color. The alleles are polymorphic in the population, with f(C1) = 0.80 and f(C2) = 0.20. Flowers that are C1C1 are yellow, orange flowers are C1C2, and C2C2 flowers are red. A storm blows a new species of hungry insects into the meadow, and they begin to eat yellow and orange flowers but not red flowers. The predation exerts strong natural selection on the flower population, resulting in relative fitness values of C1C1 = 0.30, C1C2 = 0.60, and C2C2 = 1.0.
Assuming the population begins in H-W equilibrium, what are the allele frequencies after one generation of natural selection?

1
Step 1: Begin by recalling the Hardy-Weinberg equilibrium principle, which states that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary forces. However, in this case, natural selection is acting on the population, so we need to calculate the new allele frequencies after selection.
Step 2: Write down the initial allele frequencies: f(C₁) = 0.80 and f(C₂) = 0.20. Use these to calculate the genotype frequencies under Hardy-Weinberg equilibrium. The genotype frequencies are: f(C₁C₁) = (f(C₁))², f(C₁C₂) = 2 × f(C₁) × f(C₂), and f(C₂C₂) = (f(C₂))².
Step 3: Multiply each genotype frequency by its relative fitness value to account for the effects of natural selection. The relative fitness values are given as: w(C₁C₁) = 0.30, w(C₁C₂) = 0.60, and w(C₂C₂) = 1.0. This gives the weighted genotype frequencies: f'(C₁C₁) = f(C₁C₁) × w(C₁C₁), f'(C₁C₂) = f(C₁C₂) × w(C₁C₂), and f'(C₂C₂) = f(C₂C₂) × w(C₂C₂).
Step 4: Normalize the weighted genotype frequencies to ensure they sum to 1. This is done by dividing each weighted genotype frequency by the total sum of all weighted genotype frequencies: f'(C₁C₁) / (f'(C₁C₁) + f'(C₁C₂) + f'(C₂C₂)), f'(C₁C₂) / (f'(C₁C₁) + f'(C₁C₂) + f'(C₂C₂)), and f'(C₂C₂) / (f'(C₁C₁) + f'(C₁C₂) + f'(C₂C₂)).
Step 5: Calculate the new allele frequencies after selection. The frequency of allele C₁ is given by: f(C₁) = f'(C₁C₁) + 0.5 × f'(C₁C₂), and the frequency of allele C₂ is given by: f(C₂) = f'(C₂C₂) + 0.5 × f'(C₁C₂). These are the allele frequencies after one generation of natural selection.

This video solution was recommended by our tutors as helpful for the problem above
Video duration:
2mPlay a video:
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Codominance
Codominance is a genetic scenario where two different alleles at a locus are both expressed in the phenotype of a heterozygote. In this case, the alleles C1 and C2 produce distinct flower colors when present together (C1C2 results in orange flowers), allowing for a clear understanding of how these alleles interact and contribute to the overall phenotype in the population.
Recommended video:
Guided course
Variations on Dominance
Natural Selection
Natural selection is a fundamental mechanism of evolution where individuals with traits better suited to their environment tend to survive and reproduce more than those with less advantageous traits. In this scenario, the predation of yellow and orange flowers by insects leads to differential survival based on flower color, impacting the allele frequencies in the next generation.
Recommended video:
Guided course
Natural Selection
Hardy-Weinberg Equilibrium
Hardy-Weinberg equilibrium describes a theoretical state in a population where allele frequencies remain constant from generation to generation in the absence of evolutionary influences. This concept provides a baseline to compare against after natural selection occurs, allowing for the calculation of new allele frequencies based on the relative fitness of the genotypes in the population.
Recommended video:
Guided course
Hardy Weinberg
Related Videos
Related Practice
Textbook Question
Cystic fibrosis (CF) is the most common autosomal recessive disorder in certain Caucasian populations. In some populations, approximately 1 in 2000 children have CF. Determine the frequency of CF carriers in this population.
700
views