Overview
This lecture covers the basics of population genetics, focusing on allele and genotype frequencies, Hardy-Weinberg equilibrium, and their mathematical applications in understanding population structure.
Introduction to Population Genetics
- Population genetics studies genetic composition of populations and changes over time.
- A population is a group of interbreeding organisms of the same species.
- Genetic variation exists within populations due to different alleles and genotypes.
Hardy-Weinberg Principle
- Hardy-Weinberg equilibrium states allele and genotype frequencies stay constant if no evolutionary forces act.
- Five assumptions: no selection, no mutation, no migration, large population size, random mating.
- Real populations rarely meet all five conditions; deviations indicate evolutionary change.
Allele and Genotype Frequencies
- Allele frequency: proportion of a specific allele in the population.
- Genotype frequency: proportion of a specific genotype in the population.
- Dominant and recessive alleles are denoted as p (dominant) and q (recessive).
Hardy-Weinberg Equations
- Allele frequencies: p + q = 1.
- Genotype frequencies: p² + 2pq + q² = 1.
- p²: homozygous dominant genotype frequency.
- 2pq: heterozygous genotype frequency.
- q²: homozygous recessive genotype frequency.
- Dominant alleles are not always more common than recessive alleles.
Sample Problem Process
- Use genotype data, especially for recessive traits, to determine q².
- Take the square root of q² to find q, then calculate p using p + q = 1.
- Use p and q to calculate genotype frequencies with p² + 2pq + q² = 1.
- Always check that frequencies sum to 1 for accuracy.
Tips for Solving Hardy-Weinberg Problems
- Use calculator for complex numbers and round as needed.
- Use only unambiguous genotype information for calculations.
- Double-check that all calculated frequencies add up to 1.
- Practice with additional problems to build skills.
Key Terms & Definitions
- Allele frequency — Proportion of a specific allele among all alleles in a population.
- Genotype frequency — Proportion of a specific genotype among all individuals in a population.
- Hardy-Weinberg equilibrium — Condition where allele and genotype frequencies remain constant in the absence of evolutionary forces.
- p — Frequency of the dominant allele.
- q — Frequency of the recessive allele.
Action Items / Next Steps
- Complete practice exercises and assignments provided at IPB.
- Review and solve additional Hardy-Weinberg equilibrium problems.