1. Hardy-Weinberg Principle
Hardy-Weinberg - original proportions of genotypes in a population will remain constant from generation to generation
Sexual reproduction (meiosis and fertilization) alone will not change allelic (genotypic) proportions.

2. Hardy-Weinberg Equilibrium
Population of cats
n=100
16 white and 84 black
bb = white
B_ = black
Can we figure out the allelic frequencies of individuals BB and Bb?

3. Hardy-Weinberg Principle
Necessary assumptions
Allelic frequencies would remain constant if…
population size is very large
random mating
no mutation
no gene input from external sources
no selection occurring

4. Hardy-Weinberg Principle
Calculate genotype frequencies with a binomial expansion
(p+q)2 = p2 + 2pq + q2
p2 = individuals homozygous for first allele
2pq = individuals heterozygous for alleles
q2 = individuals homozygous for second allele

5. Hardy-Weinberg Principle
p2 + 2pq + q2
and
p+q = 1 (always two alleles)
16 cats white = 16bb then (q2 = 0.16)
This we know we can see and count!!!!!
If p + q = 1 then we can calculate p from q2
Q = square root of q2 = q √ q=0.4
p + q = 1 then p = .6 ( = 1)
P2 = .36
All we need now are those that are heterozygous (2pq) (2 x .6 x .4)=0.48

6. Hardy-Weinberg Equilibrium

7. Five Agents of Evolutionary Change
Mutation
Mutation rates are generally so low they have little effect on Hardy-Weinberg proportions of common alleles.
ultimate source of genetic variation
Gene flow
movement of alleles from one population to another
tend to homogenize allele frequencies

8. Five Agents of Evolutionary Change
Nonrandom mating
assortative mating - phenotypically similar individuals mate
Causes frequencies of particular genotypes to differ from those predicted by Hardy-Weinberg.

9. Five Agents of Evolutionary Change
Genetic drift – statistical accidents.
Frequencies of particular alleles may change by chance alone.
important in small populations
founder effect - few individuals found new population (small allelic pool)
bottleneck effect - drastic reduction in population, and gene pool size

10. Genetic Drift - Bottleneck Effect

11. Five Agents of Evolutionary Change
Selection – Only agent that produces adaptive
evolutionary change
artificial - breeders exert selection
natural - nature exerts selection
variation must exist among individuals
variation must result in differences in numbers of viable offspring produced
variation must be genetically inherited
natural selection is a process, and evolution is an outcome

12. Five Agents of Evolutionary Change
Selection pressures:
avoiding predators
matching climatic condition
pesticide resistance

13. Measuring Fitness
Fitness is defined by evolutionary biologists as the number of surviving offspring left in the next generation.
relative measure
Selection favors phenotypes with the greatest fitness.

14. Interactions Among Evolutionary Forces
Levels of variation retained in a population may be determined by the relative strength of different evolutionary processes.
Gene flow versus natural selection
Gene flow can be either a constructive or a constraining force.
Allelic frequencies reflect a balance between gene flow and natural selection.

15. Natural Selection Can Maintain Variation
Frequency-dependent selection
Phenotype fitness depends on its frequency within the population.
Negative frequency-dependent selection favors rare phenotypes.
Positive frequency-dependent selection eliminates variation.
Oscillating selection
Selection favors different phenotypes at different times.

16. Heterozygote Advantage
Heterozygote advantage will favor heterozygotes, and maintain both alleles instead of removing less successful alleles from a population.
Sickle cell anemia
Homozygotes exhibit severe anemia, have abnormal blood cells, and usually die before reproductive age.
Heterozygotes are less susceptible to malaria.

17. Sickle Cell and Malaria

18. Forms of Selection
Disruptive selection
Selection eliminates intermediate types.
Directional selection
Selection eliminates one extreme from a phenotypic array.
Stabilizing selection
Selection acts to eliminate both extremes from an array of phenotypes.

19. Kinds of Selection

20. Selection on Color in Guppies
Guppies are found in small northeastern streams in South America and in nearby mountainous streams in Trinidad.
Due to dispersal barriers, guppies can be found in pools below waterfalls with high predation risk, or pools above waterfalls with low predation risk.

21. Evolution of Coloration in Guppies

22. Selection on Color in Guppies
High predation environment - Males exhibit drab coloration and tend to be relatively small and reproduce at a younger age.
Low predation environment - Males display bright coloration, a larger number of spots, and tend to be more successful at defending territories.
In the absence of predators, larger, more colorful fish may produce more offspring.

23. Evolutionary Change in Spot Number

24. Limits to Selection
Genes have multiple effects
pleiotropy
Evolution requires genetic variation
Intense selection may remove variation from a population at a rate greater than mutation can replenish.
thoroughbred horses
Gene interactions affect allelic fitness
epistatic interactions