Hardy-Weinberg Principle

Introduction

• Builds on allele frequency.
• Useful for predicting genotype frequencies: homozygous recessive, homozygous dominant, or heterozygote.

Assumptions for Stable Allele Frequency

1. No Selection: No advantage for any allele in reproduction.
2. No Mutation: Alleles don't mutate into another form or new trait.
3. Large Populations: Ensures stable allele frequencies, unlike small populations where frequencies can change easily.

Basic Equation

• Dominant allele frequency = p
• Recessive allele frequency = q
• p + q = 1 (total allele frequency must add up to 100% or 1)

Mathematical Expansion

• Squaring both sides:
  • ( (p + q)^2 = 1^2 )
  • Results in:
    • ( p^2 + 2pq + q^2 = 1 )

Interpreting the Terms

1. ( p^2 )

   • Represents probability of being homozygous dominant (BB).
   • Probability of receiving dominant allele from both parents.

2. ( q^2 )

   • Represents probability of being homozygous recessive (bb).
   • Probability of receiving recessive allele from both parents.

3. ( 2pq )

   • Represents probability of being a heterozygote (Bb).
   • Two ways to be heterozygote:
     • Dominant from one parent, recessive from another.
     • Recessive from one parent, dominant from another.

Conclusion

• This principle helps in understanding allele frequencies and genotype distribution in large populations.
• All genotype probabilities must add up to 1 (100%).

Next Steps

• Application of Hardy-Weinberg equation to derive interesting population results (covered in the next video).