1. The Evolution of Populations

2. Population genetics
Population: a localized group of individuals belonging to the same species
Species: a group of populations whose individuals have the potential to interbreed and produce fertile offspring
Gene pool: the total aggregate of genes in a population at any one time
Population genetics: the study of genetic changes in populations
“Individuals are selected, but populations evolve.”

3. Microevolution
Microevolution is a change in the frequency of alleles in a gene pool over a relatively short period.
Macroevolution replacement of one species by another

4. The Hardy-Weinberg Law
Frequency of alleles in a population will remain the same (equilibrium) if 5 conditions are met.
5 conditions:
1- Very large population size
2- No migration
3- No net mutations
4- Random mating
5- No natural selection

5. Microevolution proven by Hardy-Weinberg
Conditions are rarely met
Factors that violate the conditions listed cause evolution
Allele frequencies change from generation to generation
Indicates evolution has occurred
A Hardy-Weinberg equilibrium provides a baseline by which to judge whether evolution has occurred.

6. Hardy-Weinberg Equation
A way of calculating the frequency of alleles in a population.
p = frequency of one allele (A)
q = frequency of the other allele (a)
p + q = 1.0
p = 1 - q
q = 1 - p
p2 = frequency of AA genotype
2pq = frequency of heterozygous genotype
q2 = frequency of aa genotype
p2 + 2pq + q2 = 1.0

7. Variations Variations fall into the category of microevolution.
Take on many different forms:
Physical, Behavioral, Biochemical, etc…
Physical differences in the face of humans.
The variety in dog’s ability of scent.
Bulls and their aggressive behavior

8. Sources of variation? Mutation Genetic Drift Bottleneck Founder effect
Gene flow
Genetic recombination
Natural Selection

9. Mutations: A change in an organism’s DNA
Original source of genetic variation

11. Genetic drift:
Change in allele frequency within a gene pool of a small population from generation to generation due to chance

12. The Bottleneck Effect:
Type of genetic drift
Results from a reduction in population
The surviving population is no longer possesses all of the genes of the original population

13. Founder Effect:
A cause of genetic drift attributable to colonization by a limited number of individuals from a parent population.

14. Gene Flow:
Genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

15. Genetic recombination: (Sexual Reproduction)
Inc. variation by reshuffling genetic info
Random mating involves individuals pairing by chance
Trees releasing pollen
Nonrandom mating involves individuals selecting a mate
Inbreeding can occur if options of mates are limited
Allows normally hidden genes to be expressed in the phenotype due to recessive mutations coming together

16. Sexual selection
Sexual dimorphism: secondary sex characteristic distinction
Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

17. Natural Selection: Differential success in reproduction
Conditions in nature favor reproduction of most “fit”
Only form of microevolution that adapts a population to its environment

18. 3 types of Natural selection
1. Directional
2. Diversifying
3. Stabilizing

19. Stabilizing Selection
Favors the intermediate phenotype.
Extremes are selected against.
Infants weighing significantly less or more than 7.5 pounds have higher rates of infant mortality.
Selection works against both extremes.

20. Directional Selection
Favors phenotypes at one extreme of the range of variation.
Insecticide resistance is an example.
Only those insects resistant to an insecticide survive, leading to populations resistance.
The resistance of many bacterial species to antibiotics.
Over 200 species show some degree of antibiotic resistance.

21. Disruptive Selection
Favors extremes of variation: selection is against the middle of the curve.
Causing two or more distinct phenotypes.
The African swallowtail butterfly (Papilo dardanus) produces two distinct morphs, both resemble brightly colored but distasteful butterflies of other species.
Each morph gains protection from predation although it is in fact quite edible.

22. Population variation
Polymorphism: coexistence of 2 or more distinct forms of individuals (morphs) within the same population
Geographical variation: differences in genetic structure between populations (cline)

23. Variation preservation
Prevention of natural selection’s reduction of variation
Diploidy nd set of chromosomes hides variation in the heterozygote
Balanced polymorphism heterozygote advantage is where a heterozygous genotype is favored over either homozygous (hybrid vigor; i.e., malaria/sickle-cell anemia, cholera/cystic fibrosis) frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i.e., parasite/host)