HARDY-WEINBERG

Hardy-Weinberg Theorem

• The Hardy-Weinberg Theorem models the genetic variation in populations.
• Transitions from individual genetics to population genetics are crucial for understanding evolution.

Key Definitions

• Alleles: Variants of a gene that can lead to different traits.
• Genotypes: The genetic constitution of an individual, which can be homozygous or heterozygous.
• Population Genetics: The study of allele distribution and allele frequency changes in populations.

Allele and Genotype Frequencies

• Alleles:

• p: Frequency of dominant allele

• q: Frequency of recessive allele

• Equation: p + q = 1

• Genotypes:

• p²: Frequency of homozygous dominant genotype

• 2pq: Frequency of heterozygous genotype

• q²: Frequency of homozygous recessive genotype

• Equation: p² + 2pq + q² = 1

Probability of Alleles

• The probability of a gamete carrying a某allele equals the frequency of that allele in the population.
• Example: If p = 0.80 (dominant allele), then q = 0.20 (recessive allele).

Extending the Theorem

• For more than two alleles, the equations change:
• Three alleles:
  • (p + q + r)² = p² + 2pq + q² + 2qr + r² + 2pr = 1
• Four alleles:
  • (p + q + r + s)² = p² + 2pq + q² + 2qr + r² + 2pr + s² + 2ps + 2qs + 2rs = 1

Application: Wildflower Example

• In a population of 500 wildflowers:
• 320 red flowers
• 160 pink flowers
• 20 white flowers
• Determine allele frequencies:
• f(CR) and f(CW) represent the frequencies of respective alleles.
• Use total alleles to calculate individual allele frequencies.

Hardy-Weinberg Equilibrium

• The Hardy-Weinberg equilibrium posits that evolution does not occur when certain conditions are met:
• Population is infinitely large
• No migration
• No mutation
• No selection
• The equilibrium serves as a 'null model'; deviations suggest evolutionary processes are occurring.

Disruptions to HW Equilibrium

• When populations deviate from Hardy-Weinberg equilibrium, it indicates potential violations of its assumptions.
• Example:
• HgbS gene: A mutation affecting sickle cell disease resistance to malaria.
• Researchers investigate specific assumptions violated when examining populations not in equilibrium.

Conclusion

• The Hardy-Weinberg Theorem is essential for understanding genetic variation and population genetics. It provides a fundamental framework for studying evolution and the factors that influence genetic diversity in populations.