Question

In a population of plants, the allele for long stems is completely dominant over the allele for short stems. If 35% of the population has short stems, calculate the percentage of the population that is expected to be heterozygous

Answer 1

Assumptions:
1. Equilibrium has been reached for the allele proportions
2. Absence of evolutionary influences such as mate choice, mutation, selection, genetic drift, gene flow and meiotic drive.

Defining L=long stem, l=short stem, and L is dominant over l.
f(x) = frequency of allele x  (expressed as a fraction of population)
Then the Hardy-Weinberg equilibrium law applies:
p^2+2pq+q^2=1
where 
f(LL)=p^2
f(Ll)=2pq
f(ll)=q^2

Given f(ll)=0.35=q^2, we have
q=sqrt(0.35)=0.591608
p=1-q=0.408392
=>
f(Ll)
=2pq
=2*0.408392*0.591608=0.483216
= proportion of heterozygous population

Answer: percentage of heterozygous population is 48.32%