Background: The Hardy-Weinberg principle states is if a population is at equilibrium the allele frequencies stay constant and the population isn’t evolving. There are five conditions that have to be met for a population not to be evolving. List them below.
Condition 1:
Condition 2:
Condition 3:
Condition 4
Condition 5
The Hardy-Weinberg equilibrium is seldom reached completely, thus leading to constant state allele shifting, which leads to microevolution. The Hardy-Weinberg equation can be used to predict if a population is indeed evolving.
The Hardy-Weinberg equation is as follows.
P
2
+ 2PQ + Q
2
= 1
Where P = Dominant alleles and Q = Recessive Alleles
Steps to solving the Hardy-Weinberg Problems
1. Determine the Phenotype given. (Dominant or Recessive)
2. Determine Q. (Why? Well there is only one possible genotype associated with the recessive trait vs two genotypes associated with the dominant phenotype. This will make sense as you work through a few problems)
To find Q you first take the total number of recessive phenotypes divided by the total population. This will give you a decimal (Q 2 ). You will then need to find the square root of this decimal which will be (Q).
3. Determine P. Since we are assuming the traits only have two alleles and follow simple dominant and recessive patterns then we already know P based on the amount of Q. (1 – Q = P)
4. After you have found both P and Q you will be able to find the allele frequencies for all three possible genotypes.
Dominant Homozygous + Heterozygous + Recessive Homozygous = 1
Example .32 + .64 + .04 = 1
(Numbers are the allele frequencies for each genotype)
5. To determine if a population is evolving one needs to figure out the initial allele frequencies and find out the new allele frequencies. If there is a change, the population is undergoing microevolution.

Problem Set
1. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population to be heterozygous?
_______________ + ________________ + _________________ = 1
Answer. ______ % Heterozygous
2. If the above scenario was the original allele frequencies of a population and a flood occurred wiping out 100 organisms. The survey of individuals after the flood showed 36 of the 100 individuals left over expressed the recessive phenotype. What are the new allele frequencies and is microevolution occurring? If so what is the phenomenon that caused the evolution to occur?
_______________ + ________________ + _________________ = 1
Answer. ______ % Heterozygous
3. Lets say that brown fur coloring is dominant to gray fur coloring in mice. If you have 168 brown mice in a population of 200 mice ...
A. % Heterozygous = ________
B. % Homozygous Dominant = ________
C. % Homozygous Recessive = ________
4. If 81% of a population is homozygous recessive for a given trait …
A. % Heterozygous = ________
B. % Homozygous Dominant = ________
C. % Homozygous Recessive = ________
5. If 51% of the population carries at least one copy of the recessive allele …
A. % Heterozygous = ________
B. % Homozygous Dominant = ________
C. % Homozygous Recessive = ________