1. Main Points of Darwin’s Theory of Natural Selection
Over production. Most organisms produce more offspring than can survive.
Competition. Organisms compete for food and resources.
Variation.
There is variation among individuals of a species.
Adaptation.
Individuals with traits best suited to the environment will survive.

2. How Gene Frequencies Change
Sources of Variation
Ways that new adaptations and gene frequencies arise
S – sexual reproduction
C – crossing over during meiosis (recombination of genes)
A – arrangement of chromosomes (alleles) during meiosis
M – mutations of DNA

3. KEY CONCEPT
Evolution by Natural Selection, causes changes in POPULATIONS!

4. Population Evolution
Population genetics genetic principles as they apply to entire populations of organisms
Population group of organisms of the same species living in the same area
Genotype the representation
on the gene of an organism
Phenotype the physical trait
shown by a genotype
Allele  different form of a gene
Gene pool combined genetic
info. for all members of a
population

5. Population Genetics
Natural selection acts on individual’s phenotypes not genotypes.
Populations evolve
Individual’s genes will stay the same
Population’s gene pool may change over time due to Natural Selection
Remember, population, NOT individual evolves…
Individual’s genes stay the same
but genes w/in a population may change
Gene pool: the entire collection of genes among a population
Each new offspring in a population draws its genes from the same gene pool.
Allele frequencies  % of an allele in a population (determines frequencies of genotypes & phenotypes in populations) 5

6. Population Genetics
Which trait was a better adaptation and selected for?
How were frequencies of different alleles affected?

7. A) Single gene trait: controlled by single gene with two alleles
Gene Traits:
A) Single gene trait: controlled by single gene with two alleles
Examples: widow’s peak, hitchhiker’s thumb, tongue rolling

8. Most human traits are polygenic.
B) Polygenic trait: controlled by 2 or more genes, each with 2 or more alleles
Examples: height, hair color, skin color, eye color
Most human traits are polygenic.
This type of variation can cause different types of selection of one phenotype over others

9. Directional, Disruptive, and Stabilizing Selection
Three modes of Natural Selection:
Directional selection favors individuals at one end of the phenotypic range
Disruptive selection favors individuals at both extremes of the phenotypic range
Stabilizing selection favors intermediate variants and acts against extreme phenotypes
© 2011 Pearson Education, Inc.

10. Stabilizing Selection = maintains an already existing system.
Three Types of Natural Selection
Stabilizing Selection = maintains an already existing system.
> eliminates organisms that deviate from the norm.
> environment must remain unchanged.
> explains why there are “living fossils.”
> as long as environment doesn’t change, organisms won’t change.
Ginkgo Tree
Horseshoe Crab

11. Stabilizing Selection
Key
Percentage of Population
Birth Weight
Selection against both extremes keep curve narrow and in same place.
Low mortality, high fitness
High mortality, low fitness
Stabilizing Selection

12. MALARIA Directional Selection = favors one extreme or the other.
> eliminates organisms that are not in that extreme.
> eventually leads to changes in the population.
> occurs when organisms must adapt to a change in their environment.
> may develop into a RESISTANCE (the ability of an organism to withstand a harmful agent).
MALARIA

13. Directional Selection (page 398)
Food becomes scarce.
Key
Low mortality, high fitness
High mortality, low fitness
Directional Selection

14. Disruptive Selection = favors two extremes at one time.
> eliminates organisms that are more common.
> eventually leads to changes in the population.
African butterflies can range from red to blue.
The other colors are eaten more often resulting in a selection in favor of the extreme colors.
The red and blues are foul-tasting to predators.

15. Disruptive Selection (pg 399)
Largest and smallest seeds become more common.
Number of Birds in Population
Beak Size
Population splits into two subgroups specializing in different seeds.
Key
Low mortality, high fitness
High mortality, low fitness

18. ORGIN OF SPECIES
What is a Species? A Group of interbreeding organisms that can produce fertile offspring.

19. The Origin of Species (Macroevolution)
the formation of new species between organisms (speciation) and accompanying events
Microevolution
refers to changes in allele frequencies in a gene pool from generation to generation. Represents a gradual change in a population. 19

20. Macroevolution Microevolution

21. How Do New Species Form? Speciation- formation of a new species
Causes of Speciation:
Geographic Isolation
Temporal Isolation
3. Behavioral Isolation
4. Ecological Isolation

22. Physical separation of members of a population
Geographic Isolation
Physical separation of members of a population
(by formation of a canyon, mountain, river, etc.)
Leads to different adaptations on each side of barrier, and eventually new species (allopatric speciation)

23. Geographic Isolation = New Species: An Example
2 Species of Squirrels Formed
When They Were Separated By
The Grand Canyon

24. Temporal Isolation
Species isolated because they reproduce in different seasons or times of day
Prevents species from ever breeding together – keeps two species separate but usually arises after species have formed.

25. Behavioral Isolation
Species Differ In Their Mating Rituals (e.g. different bird songs, mating colors, dances, pheromones, etc.)

26. Ecological Isolation
Species inhabit the same area, but different habitats, so they don’t encounter each other

27. Other Factors Can Affect Genetic Variation In A Population
Other factors that increase variation in the genetic material (gene pool) of a population on which natural selection acts:
Random/nonrandom mating = sexual selection
Gene traits-single/polygenic
Isolation
Genetic Drift
Fitness is the relative ability of genotypes to survive and reproduce

28. Microevolution
refers to changes in allele frequencies in a gene pool from generation to generation. Represents a gradual change in a population.
Causes of microevolution:
                       
1)  Genetic drift
Natural selection
Gene flow
(migration of genes from
one population to another)
Mutation

29. DNA frequency in a population changes simply by CHANCE not fitness
GENETIC DRIFT
DNA frequency in a population changes simply by CHANCE not fitness 29

30. 30 Types of Genetic Drift 1. Founder’s Effect
some individuals of a population colonize a new habitat
2. Bottleneck Effect
few survivors are left to reproduce 30

31. FOUNDER'S EFFECT:
some individuals of a population colonize a new habitat
ex: Columbus bringing organisms to USA
S. America: DNA Frequency
25% pink
75% red
Spain: DNA Frequency
66% pink
33% red 31

32. Bottleneck Effect:
Small representation of the original population after a catastrophic event. Alleles in gene pool are not equally represented and species may evolve.

33. HOW DOES GENETIC DRIFT AFFECT THE DIVERSITY OF A POPULATION OVER TIME?33

34. Genetic drift = decrease in DNA diversity
Genetic drift decreases diversity. In this case yellow and pink DNA are gone, and red DNA is now the majority.
Genetic drift = decrease in DNA diversity 34

35. Patterns of Evolution Convergent Evolution Divergent Evolution
Coevolution

36. Convergent Evolution
Organisms appear similar, because of similar habitat and selection pressure. These organisms aren’t closely related
Why?
Similar environments select for similar traits

37. Divergent Evolution
Adaptive
Radiation
 accumulation of differences between groups which can lead to the formation of new species; evolving from a common ancestor
Related populations or species become less and less alike

38. A Second Type Of Divergent Evolution
Artificial Selection
Humans, rather than nature, select traits

39. Coevolution
Two or more species in close association w/one another change together
Predator/Prey
Parasite/Host
Plant/Pollinator