What would be the Hardy-Weinberg equilibrium condition for a population of haploid organism?

Would it always be in Hardy-Weinberg equilibrium?

  • $\begingroup$ @Remi.b campbell biology says that a population of diploid organisms is at hardy weinberg equilibrium only when p^2 = fraction of population with homozygous dominant organisms q^2 = fraction of population with homozygous recessive organisms and 2pq = fraction of population with heterozygous organisms if this relation is not held (between the calculated and observed values) then it can be concluded that the population is evolving This is how I understood hardy weinberg principle $\endgroup$ Commented Jan 6, 2018 at 15:47
  • $\begingroup$ A) The $p^2$, $2p(1-p)$ and $(1-p)^2$ relationships hold only for bi-allelic loci in diploid populations. It is not a general result. It is obvious that, the frequency of heterozygotes in a haploid population cannot be any different from 0. B) The assumptions of HW equilibrium include absence of selection, absence of migration and infinite population size (hence absence of drift). If a population fits these assumptions, then the population is not evolving, this is true. $\endgroup$
    – Remi.b
    Commented Jan 9, 2018 at 22:38

1 Answer 1


What is HW rule?

HW rule is a rule allowing one to compute genotype frequencies from allele frequencies and vice-versa. See Solving Hardy Weinberg problems and eventually Assumptions of Hardy-Weinberg rule for more information.

HWr in haploid organisms

In haploid individuals, the genotype frequencies and the allele (or haplotype) frequencies is the exact same thing! This is because the genotype is a simple haplotype. In other words, once you have the allele frequency, you necessarily have the genotype frequencies without need for any calculation. We can consider the haploid organism would display a special case of HW rule, where there is no assumption and where

$$p = f_{A}$$

$$q = f_{B} = 1 - f_{A}$$

, where $f_{A}$ is the frequency of the genotype carrying the allele A and $p$ is the frequency of the allele A. $f_{B}$ is the frequency of the genotype carrying the allele B and $q$ is the frequency of the allele B.


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