1. SECTION 1 GENES AND VARIATION

2. What is a species? Biological species concept defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
reproductively compatible

3. a collection of individuals of the same species in a defined area
POPULATION
a collection of individuals of the same species in a defined area
GENE POOL
the combined genetic information of all the members of a particular population
common group of genes

4. Changes in populations
Evolution of populations is really measuring changes in allele frequency
all the genes & alleles in a population = gene pool
Factors that alter allele frequencies in a population
natural selection
genetic drift
founder effect
bottleneck effect
gene flow

5. Bent Grass on toxic mine site
Populations evolve
Natural selection acts on individuals
differential survival
“survival of the fittest”
differential reproductive success
who bears more offspring
genetic makeup of population changes over time
favorable traits (greater fitness) become more common
Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field
Bent Grass on toxic mine site

6. Individuals DON’T evolve!!!

7. expressed in percentages
RELATIVE FREQUENCY
the number of times that allele occurs in a gene pool compared with the number of times other alleles occur
expressed in percentages

8. Relative Frequencies of Alleles
Sample Population
Frequency of Alleles
allele for brown fur
allele for black fur
48% heterozygous black
16% homozygous black
36% homozygous brown

9. What are the main sources of genetic variation in a population?
The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction.

10. Not every mutation has a visible effect.
Mutation & Variation
Mutation creates variation
new mutations are constantly appearing
Mutation changes DNA sequence
changes amino acid sequence?
changes protein?
change structure?
change function?
changes in protein may change phenotype & therefore change fitness
Every individual has hundreds of mutations
1 in 100,000 bases copied
3 billion bases in human genome
But most happen in introns, spacers, junk of various kind
Not every mutation has a visible effect.
Some effects on subtle.
May just affect rate of expression of a gene.

11. Sex & Variation Sex spreads variation
one ancestor can have many descendants
sex causes recombination
offspring have new combinations of traits = new phenotypes
Sexual reproduction recombines alleles into new arrangements in every offspring

12. independent assortment during meiosis crossing-over during meiosis
Gene Shuffling
independent assortment during meiosis
crossing-over during meiosis
When alleles are recombined during sexual reproduction, they can produce dramatically different phenotypes. Thus, sexual reproduction is a major source of variation within many populations.

13. Variation impacts natural selection
Natural selection requires a source of variation within the population
there have to be differences
some individuals must be more fit than others

14. Frequency of Phenotype
Generic Bell Curve for Traits in a population Most people fall in the middle of the bell curve
Frequency of Phenotype
Phenotype (height)

15. KEY CONCEPT QUESTIONS
What are the main sources of inheritable variation in a population?
Mutations and sexual reproduction
How is evolution defined in genetic terms?
genetic makeup of population changes over time
favorable traits (greater fitness) become more common

16. SECTION 2 EVOLUTION AS GENETIC CHANGE

17. Natural selection affects which individuals with different phenotypes survive and reproduce and which do not
In this way, natural selection determines which alleles are passed from one generation to the next.
Any factor that causes alleles to be added to or removed from a population will change the relative frequencies of alleles.

18. Whenever an individual dies without reproducing, its genes are removed from the population.
But if an individual produces many offspring, the proportion of that individual’s genes in the gene pool will increase.
In genetic terms, evolution is any change in the relative frequencies of alleles in a population’s gene pool.
Thus, evolution acts on populations, not on individuals.

19. Take a look:
Brown is the normal color

20. A mutation for black color
Besides a mutation for red color, what other mutation occurred in the lizard population?
A mutation for black color
How does color affect the fitness of the lizards?
Both red and brown lizards are less fit than black lizards

21. What do you predict the lizard population will look like by generation 50? Explain.
The lizard population will have more black lizards, fewer brown lizards, and no red lizards by generation 50. The environment determines the favorable color.

22. As you learned earlier:
The action of multiple alleles on traits such as height produces a range of phenotypes that often fit a bell curve
The fitness of individuals close to one another on the curve will not be very different.
But fitness can vary a great deal from one end of such a curve to the other.
And where fitness varies, natural selection can act.

23. Witness to Evolution Peppered Moth dark vs. light variants

24. Peppered moth
Year % dark % light

25. Peppered moth Why did the population change?
early 1800s = pre-industrial England
low pollution
lichen growing on trees = light colored bark
late 1800s = industrial England
factories = soot coated trees
killed lichen = dark colored bark
mid 1900s = pollution controls
clean air laws
return of lichen = light colored bark
industrial melanism

26. Natural selection can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection.

27. DIRECTIONAL SELECTION
When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end

28. Ex) The supply of small seeds runs low in a particular environment
Ex) The supply of small seeds runs low in a particular environment. Take a look at the graph below and explain what is happening.
- the birds with larger beaks are more likely to survive and reproduce because their beaks are adapted to the available food. There is a shift in the beak size of a population.

29. STABILIZING SELECTION
When individuals near the center of the curve have higher fitness than individuals at either end of the curve
EX) Figure shows that human babies born at an average mass are more likely to survive than babies born either much smaller or much larger than average

31. DISRUPTIVE SELECTION
when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle
EX) average-sized seeds become less common, and larger and smaller seeds become more common. As a result, the bird population splits into two subgroups specializing in eating different-sized seeds.

33. Effects of Selection
Driving changes in a population

34. random change in allele frequencies that occurs in small populations
GENETIC DRIFT
random change in allele frequencies that occurs in small populations
In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population

35. Genetic drift Effect of chance events founder effect
small group splinters off & starts a new colony
bottleneck
some factor (disaster) reduces population to small number & then population recovers & expands again
1 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families
Genghis Khan tracked through Y chromosome.

36. Bottleneck effect
When large population is drastically reduced by a disaster
famine, natural disaster, loss of habitat…
loss of variation by chance
alleles lost from gene pool
narrows the gene pool

37. Cheetahs All cheetahs share a small number of alleles
less than 1% diversity
as if all cheetahs are identical twins
2 bottlenecks
10,000 years ago
Ice Age
last 100 years
poaching & loss of habitat

38. Genetic Drift Sample of Original Population Descendants
Founding Population A
Founding Population B

39. Genetic Drift Sample of Original Population Descendants
Founding Population A
Founding Population B

40. Genetic Drift Sample of Original Population Descendants
Founding Population A
Founding Population B

41. FOUNDER EFFECT
situation in which allele frequencies change as a result of the migration of a small subgroup of a population
Darwin’s Finches
Fruit flies on Hawaii

42. Founder effect
When a new population is started by only a few individuals
some rare alleles may be at high frequency; others may be missing
skew the gene pool of new population
human populations that started from small group of colonists
example: white people colonizing New World
Small founder group, less genetic diversity than Africans
All white people around the world are descended from a small group of ancestors
100,000 years ago
(Chinese are white people!)

43. in which allele frequencies remain constant
HARDY-WEINBERG PRINCIPLE
allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change
GENETIC EQUILLIBRIUM
in which allele frequencies remain constant
If the allele frequencies do not change, the population will not evolve

44. Five conditions are required to maintain
genetic equilibrium (alleles don’t
change) from generation to generation:
There must be random mating
The population must be very large
There can be no movement into or out of the population
No mutations
No natural selection.

45. SECTION 3 THE PROCESS OF SPECIATION

46. Speciation
New species are created by a series of evolutionary processes
REPRODUCTIVE ISOLATION
when members of two populations cannot interbreed and produce fertile offspring
populations become reproductively isolated
temporally isolated
geographically isolated
behaviorally isolated
isolated populations evolve independently

47. Geographic Isolation geographic separation migration physical barrier
Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white–tailed antelope squirrel

48. Squirrels at the Grand Canyon Darwin’s Finches
GEOGRAPHIC ISOLATION
two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Squirrels at the Grand Canyon
Darwin’s Finches

49. TEMPORAL ISOLATION
two or more species reproduce at different times
Orchids and pollination
BEHAVIORAL ISOLATION
occurs when two populations are capable of interbreeding but have differences in courtship rituals or other types of behavior
Mating songs of meadowlarks

50. Darwin studied birds on the Galapagos Islands.
He thought they were blackbirds, warblers, and other kinds of birds!
The species he examined differed greatly in the sizes and shapes of their beaks and in their feeding habits

51. Some species fed on small seeds, while others ate large seeds with thick shells. One species used cactus spines to pry insects from dead wood. One species even pecked at the tails of large sea birds and drank their blood!

52. Once Darwin discovered that these birds were all finches, he hypothesized that they had descended from a common ancestor. Over time, he proposed, natural selection shaped the beaks of different bird populations as they adapted to eat different foods

53. Darwin’s hypothesis relied on two testable assumptions.
First, in order for beak size and shape to evolve, there must be enough inheritable variation in those traits to provide raw material for natural selection.
Second, differences in beak size and shape must produce differences in fitness that cause natural selection to occur

54. Speciation of Darwin’s Finches
Founders arrive
Separation of populations
Changes in the gene pool
Reproductive isolation
Ecological competition
Continued evolution