What Do ‘p’ and ‘q’ Represent in the Hardy-Weinberg Equation? Understanding Allele Frequencies

The Hardy-Weinberg equilibrium is a fundamental concept in population genetics, providing a mathematical model to describe the genetic composition of a population that is not evolving. Central to this model are the variables ‘p’ and ‘q’, which are used in the Hardy-Weinberg equation:

p2+2pq+q2=1p2+2pq+q2=1

But what exactly do ‘p’ and ‘q’ represent in this equation?

‘p’ and ‘q’ Are Allele Frequencies

• ‘p’ represents the frequency of one allele (usually the dominant allele, such as ‘A’) in the population.

• ‘q’ represents the frequency of the other allele (usually the recessive allele, such as ‘a’) in the population.

Together, these frequencies account for all the alleles at a particular genetic locus in a population, and their sum must always equal 1:

$$p+q=1$$

Why Are These Frequencies Important?

Knowing the values of ‘p’ and ‘q’ allows geneticists to:

• Predict genotype frequencies (e.g., AA, Aa, aa) in the population.

• Detect evolutionary changes by comparing observed and expected frequencies.

• Estimate carrier rates for genetic diseases.

Not Genotype Frequencies

It’s important to note that ‘p’ and ‘q’ do not represent genotype frequencies (such as the proportion of AA, Aa, or aa individuals), but rather the proportion of each allele in the population.

Conclusion

In the Hardy-Weinberg equation for an equilibrium population, ‘p’ and ‘q’ represent allele frequencies.

Correct answer: (2) Allele frequency