1. Hardy-Weinberg Equilibrium
Tracking Microevolution in Populations

2. So, how do we know if a population is evolving?
The Hardy-Weinberg equation can be used to test whether a population is evolving
The Hardy-Weinberg principle states that allele and genotype frequencies within a sexually reproducing, diploid population will remain in equilibrium unless outside forces act to change those frequencies
This state of non-evolution is known as Hardy Weinberg Equilibrium

3. For Hardy-Weinberg Equilibrium to exist, five conditions must be met:
Very large population (to prevent what?)
No gene flow between populations
No mutations
Random mating
No natural selection
Is this likely, or even possible?

4. However, it is convenient to use the Hardy- Weinberg equation to take a snapshot of the allele and genotype frequencies in a population
Doing this over multiple generations can show if a population is evolving

5. The Hardy-Weinberg Equation
Imagine that there are two alleles in a blue-footed booby population: W and w
W is a dominant allele for a nonwebbed booby foot
w is a recessive allele for a webbed booby foot

6. The Hardy-Weinberg Equation
Consider the gene pool of a population of 500 boobies
320 (64%) are homozygous dominant (WW)
160 (32%) are heterozygous (Ww)
20 (4%) are homozygous recessive (ww)
The Hardy-Weinberg Equation

8. Frequency of dominant allele (W) = 80% = p
Equation for allele frequency in a Hardy-Weinberg population – (KEY: p = Dominant allele and q = recessive allele)
p + q = 1
Frequency of dominant allele (W) = 80% = p
80% of alleles in the booby population are W
Frequency of recessive allele (w) = 20% = q
20% of alleles in the booby population are w
Frequency of alleles must be 100% or 1.0
Equation for genotype frequency in a Hardy-Weinberg population – (KEY: p2 = homozygous dominant (WW), 2pq = heterozygous (Ww), and q2 = homozygous recessive (ww)
p2 + 2pq + q2 = 100% = 1.0
Frequency of all three genotypes must be 100% or 1.0
homozygous dominant + heterozygous + homozygous recessive = 100%

9. If we use these genotype frequencies in a Punnett square, we can predict that the next generation will have the same frequencies as the one before it

10. The Hardy Weinberg equation is useful in public health science
It is often used to determine the frequency of alleles for certain inherited diseases, such as cystic fibrosis or phenylketonuria, or PKU
These can be determined by the occurrence per number of births