1. How do we know if a population is evolving?
Hardy Weinberg Equilibrium

2. When is a population not evolving?
How do we know if a gene pool has changed?
The Hardy-Weinberg Principle can help answer these questions

3. How can a population’s genes change over time?
All of the alleles of a population’s genes together make up a gene pool
Allele frequency - percent of any specific allele in the gene pool
Genetic equilibrium – a population in which the frequency of alleles remains the same over generations

4. The Hardy-Weinberg Principle states:
Genetic equilibrium will be reached if the frequency of alleles remains stable generation after generation
Genetic equilibrium = no evolution occurring

5. Hardy-Weinberg Principle
Conditions necessary for genetic equilibrium are:
No mutation occurs
Immigration and emigration do not occur (population is isolated from other populations) - no gene flow.
Population is very large
Mating is totally random
All individuals survive and reproduce equally (no natural selection)

6. Hardy-Weinberg Principle
It is virtually impossible to meet these conditions
Allelic frequencies do change in populations, therefore evolution occurs
The main application of this principle is calculating allele and genotype frequencies in a population

7. p + q = 1 In a population, the sum frequency of alleles will equal 1
This can be expressed as:
p + q = 1
Where:
p = frequency of the dominant allele
q = frequency of recessive allele

8. Hardy-Weinberg Equation p2 + 2pq + q2 = 1
Where:
p2 = frequency of individuals homozygous dominant
2pq = frequency of heterozygous individuals
q2 = frequency of individuals homozygous recessive

9. 4 simple rules for calculating equations:
Find what q2 and q are first
They can be determined with the information given to you in a problem. The q2 population are the homozygous recessive individuals. Once you solve for q2, take the square root to find q.
Once you find what q is, you subtract that number from 1
p + q = 1. That will give you p, or the number of dominant alleles in a population
Square the p number to solve for p2
This will give you the number of homozygous dominant individuals in a population.
Now that we have p2, p, q2, and q, plug those numbers into the 2pq
Check your work by plugging into each equation and see if they equal 1

10. Question
If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population are homozygous dominant? (Recessive phenotype = homozygous genotype)
p + q = 1 p2 + 2pq + q2 = 1
q2 = = 0.49
q =
p =
p2 =
2pq =