1. The Evolution of Populations
Chapter 23
The Evolution of Populations
Natural Selection causes Evolution
Changes to environment, mutations change phenotype, phenotype changes effect fitness of organisms, human impact the environment
Directional Selection- bell shaped curve shifting direction due to an influence (like environment)
Mutation caused a red blood cell to become sickle shaped. Hetero for sickle can’t get malaria, homo for sickle cell you have sickle cell. Dark area in Africa they have sickle cell gene, so protected against malaria. Natural selection in humans. Bad to have sickle cell gene when malaria isn’t present
Multi Drug Resistant Tuberculosis. Take several doses so bacteria become resistant.

2. 5 Types of Selection
Acts to select the individuals that are best adapted for survival and reproduction; resulting in alleles being passed to the next generation in proportions different than frequencies in the present generation
Stabilizing
Disruptive (Diversifying)
Directional
Sexual
Artificial

3. Stabilizing selection: operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness. (Birth Weights)
Directional selection: An extreme trait makes an organism more fit making one phenotype replace another (Glacier Lilies/pesticides and insects)
Disruptive selection: a process that splits a population into two groups resulting in balanced polymorphism (black-bellied seed cracker finches)
Ecological Selection: Natural Selection
Change takes place in the ecosystem.
Directional- Curve moves in one direction. Glacier lilies coming out earlier in the year due to increased temperatures
Stabilizing- selection against extremes. Tiny baby, Large babies die off.
Disruptive- selection against middle, extremes do way better.

4. DIRECTIONAL SELECTION STABILIZING SELECTION
Effects of Selection
Changes in the average trait of a population
DIRECTIONAL SELECTION
STABILIZING SELECTION
DISRUPTIVE SELECTION
giraffe neck
horse size
human birth weight
rock pocket mice

5. Natural selection in action (Directional Selection)
Insecticide & drug resistance
insecticide didn’t kill all individuals
resistant survivors reproduce (selective advantage)
resistance is inherited
insecticide becomes less & less effective
The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action.
The results of application of new insecticide are typically encouraging, killing 99% of the insects.
However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases.

6. Survival doesn’t matter if you don’t reproduce!
Sexual Selection
Acting on reproductive success
attractiveness to potential mate
fertility of gametes
successful rearing of offspring
Acts in all sexually reproducing species
the traits that get you mates
sexual dimorphism (intersexual selection:
Female picks best looking male)
influences both morphology &
behavior (intrasexual selection: males
Fight, winner is more desirable to female)
can act in opposition to natural selection
Survival doesn’t matter if you don’t reproduce!

7. Artificial Selection
Humans breeding plants and animals by seeking individuals with desired traits as a breeding stock
animals, plants, etc.

8. Artificial selection This is not just a process of the past…
It is all around us today

9. “descendants” of wild mustard “descendants” of the wolf
Artificial selection
Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties”
“descendants” of wild mustard
“descendants” of the wolf

10. Preserving Variation in a Population
Balanced Polymorphism
Geographic Variation
Sexual Reproduction
Outbreeding
Diploidy
Heterozygote Advantage
Frequency-Dependent Selection
Evolutionary Neutral Traits

11. Balanced Polymorphism
The presence of two or more phenotypically distinct forms of a trait in a single population of a species.
each morph is better adapted in a different area, but both varieties continue to exist

12. Heterozygote Advantage
Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes; preserving multiple alleles in a population
Natural selection will tend to maintain two or more alleles at that locus
The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance

13. Heterozygote Advantage
In tropical Africa, where malaria is common:
homozygous dominant (normal)
die or reduced reproduction from malaria: HbHb
homozygous recessive
die or reduced reproduction from sickle cell anemia: HsHs
heterozygote carriers are relatively free of both: HbHs
survive & reproduce more, more common in population
Frequency of sickle cell allele & distribution of malaria

14. Frequency-Dependent Selection
AKA: minority advantage
decrease of the more common phenotypes, increase of the less common phenotypes
ex: predator-prey relationships allow the less common phenotypes to succeed and reproduce

15. Geographic Variation
Graded variation in the phenotype of an organism (cline): variation in appearances due to differences in environments
ex. north-south cline

16. Sexual Reproduction
Variation due to shuffling and recombination of alleles during meiosis and fertilization
independent assortment
crossing over
random fertilization

17. Outbreeding
the mating of organisms within one species that are not closely related; maintaining variation and a strong gene pool
This is true example “outbreeding”
This is one result you get when you Google Image “outbreeding”

18. Diploidy
Diploidy (2n) maintains genetic variation in the form of hidden recessive alleles, that could be advantageous when conditions change

19. Evolutionary Neutral Traits
traits that seem to have no selective advantage
ex.) blood types

20. Causes of Evolution of a Population
Genetic Drift
Bottleneck effect, flounder effect
Gene Flow
Mutations
Nonrandom Mating
Natural Selection

21. Genetic Drift
Chance events changing frequency of traits in a population
not adaptation to environmental conditions
not selection
founder effect
small group splinters off & starts a new colony
bottleneck
some factor (disaster) reduces population to small number & then population recovers & expands again but from a limited gene pool

22. albino deer Seneca Army Depot
Founder effect
When a new population is started by only a small group of individuals
just by chance 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: colonization of 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!)
albino deer Seneca Army Depot

23. Bottleneck effect
When large population is drastically reduced by a disaster
famine, natural disaster, loss of habitat…
loss of variation by chance event
alleles lost from gene pool
not due to fitness
narrows the gene pool

24. Gene Flow
the movement of alleles into or out of a population via migration of fertile individuals or gametes between populations

25. Mutations
changes in genetic material; increasing diversity either at one loci or several

26. Nonrandom Mating Rarely is mating completely random in a population.
Usually individuals mate with individuals in close proximity.
This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits

27. Forces of evolutionary change
Natural selection
traits that improve survival or reproduction will accumulate in the population
adaptive change

28. Natural Selection
Selection acts on any trait that affects survival or reproduction
predation selection
physiological selection
sexual selection

29. Measuring Evolution of Populations

30. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

31. Populations & gene pools
Concepts
a population is a localized group of interbreeding individuals
gene pool is collection of alleles in the population
remember difference between alleles & genes!
allele frequency is how common is that allele in the population
how many A vs. a in whole population

32. Evolution of populations
Evolution = change in allele frequencies in a population
Hardy Weinberg Equilibrium states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.
hypothetical: what conditions would cause allele frequencies to not change?
non-evolving population
REMOVE all agents of evolutionary change
very large population size (no genetic drift)
no migration (no gene flow in or out)
no mutation (no genetic change)
random mating (no sexual selection)
no natural selection (everyone is equally fit)
states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influence
10 people, half have red hair (homo reces)
14 red alleles, 6 dominant alleles
Red is Recessive(q= allele frequency of recessive trait) q=14/20=.7
Blue is Dominant (p= allele frequency of dominant trait) p=6/20=.3
p+q=1
In this gene pool 30% of genes are dom and 70% are reces.
What are the odds that if I pull one out it will be recessive? 7/10
what about 2? 7/10*7/10=.49 (reces)
What are the odds of pulling out a blue? 3/10
what about 2? 3/10*3/10=0.09 (dom)
What are the odds of me pulling out a blue and a red?
7/10*3/10=21/100 (red, blue)
3/10*7/10=21/100 (blue, red)
21/100+21/100=
Homo dom, hetero, homo recess (if they talk about any of these they want these)
P2+2pq+q2=1
.3^2 + 2*.3* ^2=1
If they ask for allele frequency they want just p or q’s value
EXAMPLE
16% unable to taste chemical PTC
Non-tasters are recessive
Q^2= .16
Q=.4
P=1-.4=.6
1) % of individuals in pop are tasters?
16% are nontasters, so 84% are tasters
2) Frequency of dominant and recessive allele
Q=.4 (rec), P=.6 (dom)
3) % of pop are heterozygous
2PQ= 2(.6)(.4)=.48= 48%
20% allele frequency for recessive gene
Q=.20 (rec)
P=.80 (dom)
1) % have 2 copies of gene and immune?
Q^2=.2^2=.04
2) % are less susceptible b/c hetero?
2pq=2*.8*.2=.32=32%

33. If all five conditions are met then a population is considered to be in equilibrium and NO EVOLUTION is occurring
no genetic drift
no gene flow
no nonrandom mating
no mutations
no natural selection

34. Hardy-Weinberg equilibrium
Hypothetical, non-evolving population
preserves allele frequencies
Serves as a model (null hypothesis: no relationship between two results)
natural populations rarely in H-W equilibrium
useful model to measure if forces are acting on a population
measuring evolutionary change
G.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in Their formula predicts the expected genotype frequencies using the allele frequencies in a diploid Mendelian population. They were concerned with questions like "what happens to the frequencies of alleles in a population over time?" and "would you expect to see alleles disappear or become more frequent over time?"
G.H. Hardy
mathematician
W. Weinberg
physician

35. The Hardy-Weinberg Equation
enables us to calculate frequencies of alleles in a population
p2 + 2pq + q2 = or p + q = 1
p= dominant allele
q= recessive allele A a AA Aa aa A a

36. Hardy-Weinberg theorem
Counting Alleles
assume 2 alleles = B, b
frequency of dominant allele (B) = p
frequency of recessive allele (b) = q
frequencies must add to 1 (100%), so:
p + q = 1 BB Bb bb

37. Hardy-Weinberg theorem
Counting Individuals
frequency of homozygous dominant: p x p = p2
frequency of homozygous recessive: q x q = q2
frequency of heterozygotes: (p x q) + (q x p) = 2pq
frequencies of all individuals must add to 1 (100%), so:
p2 + 2pq + q2 = 1 BB Bb bb

38. H-W formulas Alleles: p + q = 1 Individuals: p2 + 2pq + q2 = 1 B b BB

39. Using Hardy-Weinberg equation
population: 100 cats
84 black, 16 white
How many of each genotype?
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): = 0.6
p2=.36
2pq=.48
q2=.16
84 black (dom)
16 white (rec)
Q^2=16/100
Q=.4
1-.4=.6 (P)
P^2= (.6)^2= .36
2PQ= 2(.6)(.4)=.48
Q^2= .16 BB Bb bb
What are the genotype frequencies?
Must assume population is in H-W equilibrium!

40. Using Hardy-Weinberg equation
p2=.36
2pq=.48
q2=.16
Assuming H-W equilibrium BB Bb bb
Null hypothesis
p2=.20
p2=.74
2pq=.10
2pq=.64
q2=.16
q2=.16
Sampled data 1:
Hybrids are in some way weaker.
Immigration in from an external population that is predomiantly homozygous B
Non-random mating... white cats tend to mate with white cats and black cats tend to mate with black cats.
Sampled data 2:
Heterozygote advantage.
What’s preventing this population from being in equilibrium. bb Bb BB
Sampled data
How do you explain the data?
How do you explain the data?

41. Insert Practice Problems
Any Questions??
Insert Practice Problems

42. 1. Given a population in Hardy-Weinberg equilibrium with allele frequencies A =0.9 and a = 0.1, determine the frequencies of the three genotypes AA, Aa and aa.

43. 3. Allele W for white wool is dominant over allele w for black wool
3. Allele W for white wool is dominant over allele w for black wool. In a sample of 900 sheep, 891 are white and 9 are black. Estimate the allelic frequencies in this sample.

44. 6. 1 in 1,700 US Caucasian newborns have cystic fibrosis
6. 1 in 1,700 US Caucasian newborns have cystic fibrosis. C for normal is dominant over c for cystic fibrosis.
a) What percentage of the above population has cystic fibrosis (cc)?
b) Calculate the frequencies of the C and c alleles.
c) Calculate the frequencies of the normal (CC) and carrier (Cc) genotypes.
d) How many of the 1,700 population members are normal (CC)? Carriers (Cc)?
e) It has been found that a carrier is better able to survive diseases with severe diarrhea. What would happen to the frequency of the “c” if there was an epidemic of cholera or other type of diarrhea producing disease? Would “c” increase or decrease?

45. 9. In a tropical forest there is a species of bird that has a variable tail length. Long is incompletely dominant over short. In one population of 2000 birds, 614 have long tails, 973 have medium length tails, and 413 birds have short tails.
a) What is the frequency of each allele in the population?
b) Is the population in Hardy Weinberg equilibrium?
certainty

46. THE END

47. Speciation and Reproductive Isolation
Species: members in a population who have the potential to interbreed in nature and produce viable, fertile offspring
Reproductive isolation: one group of genes becomes isolated from one another to begin a separate evolutionary history
Speciation: anything that fragments a population and isolates a small group of individuals
Allopatric
Sympatric

48. Allopatric Speciation: caused by geographic isolation

49. Sympatric Speciation: caused by anything besides geographic isolation
polyploidy: a cell has two or more complete sets of chromosomes
habitat isolation: two organisms live in the same area but rarely encounter one another
behavioral isolation: two species do not mate because of differences in courtship behavior
temporal isolation: populations may mate or flower at different seasons or different times of day
reproductive isolation: closely related species unable to mate because of a variety of reasons
prezygotic barriers
postzygotic barriers
reproductive isolation

50. Patterns of Evolution Divergent Convergent Parallel Coevolution
Adaptive Radiation
Gradualism
Punctuated

51. Divergent Evolution
Occurs when a population becomes isolated from the rest of the species, exposed to new selective pressures, and evolves into a new species
allopatric speciation
sympatric speciation
Divergent evolution occurs when two species are separated by some degree (be it by distance/natural obstacles creating diffusion or by other factors) and one group of said species develops different attributes that gradually cause future generations to become differentiated enough to be considered an independent species. Despite this, the different characteristics of the species (homologous structures) are still recognizable enough to be seen as being related, even if their structure and function have changed somewhat

52. Convergent evolution Flight evolved in 3 separate animal groups
evolved similar “solution” to similar “problems”
analogous structures

53. & sleek bodies are analogous structures!
Convergent evolution
Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to life in the sea
not closely related
Those fins & tails
& sleek bodies are analogous structures!

54. Parallel Evolution Convergent evolution in common niches marsupial
filling similar ecological roles in similar environments, so similar adaptations were selected
but are not closely related
marsupial
mammals
placental
mammals

55. Parallel types across continents
Niche
Placental Mammals
Australian Marsupials
Burrower
Mole
Anteater
Mouse
Lemur
Flying
squirrel
Ocelot
Wolf
Tasmanian “wolf”
Tasmanian cat
Sugar glider
Spotted cuscus
Numbat
Marsupial mole
Marsupial mouse
Nocturnal
insectivore
Climber
Glider
Stalking
predator
Chasing

56. Coevolution
Two or more species reciprocally affect each other’s evolution
predator-prey
disease & host
competitive species
mutualism
pollinators & flowers

57. Adaptive Radiation
the emergence of numerous species from a common ancestor introduced into an environment, filling a niche