1. Population genetics and Hardy-Weinberg
Section 27.3 – Nov 18, 2014

2. Population genetics
Individuals CANNOT evolve – evolution happens at population level
Genetic changes occur within a population over generations = phenotypic changes
Microevolution – change in gene frequencies within a population over time

3. Population genetics
 Population – all members of a single species that occupy a certain area and breed together
Example of two different populations??
Gene pool – (following Mendel’s laws) the total number of alleles at all the gene loci in all members (that are capable of sexual reproduction)

4. Hardy-Weinberg Equilibrium
p2 + 2pq + q2 = 1
p2 = frequency of DD genotype (homozygous dominant)
2pq = frequency of Dd genotype (heterozygous)
q2 = frequency of dd genotype (homozygous recessive)

5. Hardy-Weinberg Equilibrium
Example:
Uses Punnett squares to determine genotype frequencies

6. Hardy-Weinberg Equilibrium
“allele frequencies in a gene pool will remain at equilibrium, and thus constant after one generation of random mating in a large, sexually reproducing population as long as five conditions are met”
No mutations
No genetic drift
No gene flow
Random mating
No selection
Why is it that in real life these conditions are almost NEVER met?

7. Hardy-Weinberg Equilibrium
Hardy-Weinberg equilibrium states that allele frequencies in a gene pool within a population do not change
If they do change = microevolution
Use Hardy-Weinberg to detect deviations from equilibrium
Deviations suggest that one or more of the five conditions is occurring

8. Example: Moths

9. Example
In some areas of Africa, the recessive sickle-cell allele has a frequency of 0.3. The frequency of the normal hemoglobin allele is calculated as:
1-0.3 = 0.7
0.72 = 0.49 =SS
2(0.7)(0.3) =0.42 = Ss (42% of the population)
0.32 = 0.09 = ss (9% of the population affected by
sickle-cell anemia)
= 1 p p2
2pq q2

10. Complete “Check Your Progress” pg. 552 #1-2 Handouts
Hardy-Weinberg explained by Yogi Bear
Hardy-Weinberg Problems

11. Some people think that the dominant allele of a gene should constantly increase in frequency in a population, and quickly force out the recessive allele.
Use the Hardy-Weinberg principle and/or equation to explain why this idea is incorrect. What false assumptions could cause people to have this incorrect idea?