1. Natural Selection Major mechanism of evolution
Environment is always changing
Acts upon the phenotype of the population
Based on Darwin’s idea that resources are limited and that there is competition for those resources.
Adaptation = a genetic variation favored by natural selection.
When allele frequencies shift, speciation occurs
Thus, the frequency change is NOT RANDOM

2. 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

4. Natural selection in action
Insecticide & drug resistance
insecticide didn’t kill all individuals
resistant survivors reproduce
resistance is inherited
insecticide becomes less & less effective
Resistance…
NOT immunity!
MRSA

5. Heterozygote Advantage
Keeps the recessive allele in the population
Ex: Sickle Cell Anemia
aa – dies of sickle cell anemia
Aa – some side affects BUT resistant to malaria!
AA – no disease present BUT prone to malaria

6. Hidden variations can be exposed through selection!
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower cluster
Leaves
Cauliflower
Flower
and
stems
Broccoli
Wild mustard
Kohlrabi
Stem
Kale
Artificial selection

7. In addition to natural selection, evolutionary change is also driven by random processes…

8. 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
it’s random who joins the group
bottleneck
a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool
who survives disaster may be random
Founders: 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. Ex: human populations that started from small group of colonists
example: colonization of New World
Bottleneck: 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

9. Ex: Cheetahs All cheetahs share a small number of alleles
less than 1% diversity
2 bottlenecks
10,000 years ago
Ice Age
last 100 years
poaching & loss of habitat

10. Peregrine Falcon
Conservation issues
Bottlenecking is an important concept in conservation biology of endangered species
loss of alleles from gene pool
reduces variation
reduces adaptability
Breeding programs must consciously outcross
Golden Lion Tamarin

11. Human Impact on variation
How do we affect variation in other populations?
Artificial selection/Inbreeding
Animal breeds
Loss of genetic diversity
Insecticide usage
Overuse of antibiotics
resistant bacterial strains

12. Hardy Weinberg: Population Genetics
Using mathematical approaches to calculate changes in allele frequencies…this is evidence of evolution.

13. Hardy-Weinberg equilibrium
Hypothetical, non-evolving population
preserves allele frequencies
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

14. Evolution of populations
Evolution = change in allele frequencies in a population
hypothetical: what conditions would cause allele frequencies to not 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)
H-W occurs ONLY in non-evolving populations!

15. 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

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

17. Hardy-Weinberg theorem
Frequencies are usually written as decimals!
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

18. 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

19. 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 BB Bb bb
Must assume population is in H-W equilibrium!
What are the genotype frequencies?

20. Using Hardy-Weinberg equation
p2=.36
2pq=.48
q2=.16
Assuming H-W equilibrium:
Expected data BB Bb bb
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
Observed data
How do you explain the data?
How do you explain the data?

21. Origin of the Equation p2 + 2pq + q2
Assuming that a trait is recessive or dominant
Allele pairs AA, Aa, aa would exist in a population
p + q = 1
The probability that an individual would contribute an A is called p
The probability that an individual would contribute an a is called q
Because only A and a are present in the population the probability that an individual would donate one or the other is 100%
p2 + 2pq + q2
Male Gametes A(p)
Male Gametes a(q)
Female gametes A(p) AA p2 Aa pq
Female Gametes a(q) aa q2

22. Example of an evolving population:
Peppered moth
Variation of colors in the population existed (Black, Peppered, White)
As environmental conditions changed the frequency of the recessive allele increased.
This was seen as an adaptation to the environment that allowed the species to continue to live.

23. There’s something you need to know…
The Origin of Species
Mom, Dad…
There’s something you need to know…
I’m a MAMMAL!

24. Speciation
Changes in allele frequency are so great that a new species is formed
Can be slow and gradual or in “bursts”
Extinction rates can be rapid and then adaptive radiation follows when new habitats are available

25. Correlation of speciation to food sources
Seed eaters
Flower eaters
Insect eaters
Rapid speciation: new species filling niches, because they inherited successful adaptations.
Adaptive radiation

26. So…what is a species?
Population whose members can interbreed & produce viable, fertile offspring
Reproductively compatible
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark 26

27. How do new species originate?
When two populations become reproductively isolated from each other.
Speciation Modes:
allopatric
geographic separation
“other country”
sympatric
still live in same area
“same country”

28. Allopatric Speciation
Physical/geographical separation of two populations
Allele frequencies diverge
After a length of time the two populations are so different that they are considered different species
If the barrier is removed interbreeding will still not occur due to pre/post zygotic isolation

29. Sympatric Speciation
Formation of a new species without geographic isolation.
Causes:
Pre-zygotic barriers exist to mating
Polyploidy (only organism with an even number of chromosomes are fertile…speciation occurs quickly)
Hybridization: two different forms of a species mate in common ground (hybrid zone) and produce offspring with greater genetic diversity than the parents….eventually the hybrid diverges from both sets of parents

30. Sympatric Speciation
Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

31. Pre-zygotic Isolation
Sperm never gets a chance to meet egg
Geographic isolation: barriers prevent mating
Ecological isolation: different habitats in same region
Temporal isolation: different populations are fertile at different times
Behavior Isolation: they don’t recognize each other or the mating rituals
Mechanical isolation: morphological differences
Gamete Isolation: Sperm and egg do not recognize each other
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

32. PRE-Zygotic barriers
Obstacle to mating or to fertilization if mating occurs
geographic isolation
ecological isolation
temporal isolation
behavioral isolation
mechanical isolation
gametic isolation

33. Post Zygotic Isolation
Hybrid Inviability – the embryo cannot develop inside the mothers womb
Hybrid Sterility – Adult individuals can be produced BUT they are not fertile
Hybrid Breakdown – each successive generation has less fertility than the parental generation
Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.
Even if hybrids are vigorous they may be sterile; chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Horse(64) x donkey(62) = mule (63 chromosomes)
In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.
On path to separate species.

34. Evolutionary Time Scale
Microevolution – changing of allele frequencies in a population over time.
Macroevolution – patterns of change over geologic time. Determines phylogeny
Gradualism – species are always slowly evolving
Punctuated equilibrium – periods of massive evolution followed by periods with little to no evolution

35. Patterns of Evolution Divergent Evolution (adaptive radiation)
Convergent Evolution
Two or more species that share a common environment but not a common ancestor evolve to be similar
Is it a shark or a dolphin??

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

37. Mass Extinctions
At least 5 mass extinctions have occurred throughout history.
Possible causes: dramatic climate changes occurring after meteorite collisions and/or continents drift into new and different configurations.

38. What must Earth have been like before living things took over?
Origin of the Earth
What must Earth have been like before living things took over?

39. The Primitive Earth Atmosphere:
All chemicals/compounds necessary are thought to have originated on earth
Inorganic precursors:
Water vapor
Nitrogen
Carbon dioxide
Small amounts of hydrogen and carbon monoxide
These were the monomers for forming more complex molecules.
Experiments have shown that it is possible to form organic from inorganic.

40. Origin of Organic Molecules
Water vapor
Condensed liquid with complex, organic
molecules
Condenser
Mixture of gases
("primitive
atmosphere")
Heated water
("ocean")
Electrodes discharge sparks
(lightning simulation)
Water
Origin of Organic Molecules
Abiotic synthesis
Oparin
first molecules formed by strong energy sources
Miller & Urey test hypothesis
formed organic compounds
amino acids
adenine
CH4 H2
NH3
Attempted to prove that chemical evolution could occur
The experiment
Used water, methane, ammonia, hydrogen sealed inside a glass container
Water was heated to produce steam and sparks were generated from electrodes
Water was then cooled and allowed to condense\
Experiment went on in this cycle for 1 week
Results
15% of carbon was now present in the form of organic materials
13 out of 20 amino acids were present
High concentrations of the base Adenine were also detected

41. Key Events in Origin of Life
Origin of Cells (Protobionts)
lipid bubbles  separate inside from outside
 metabolism & reproduction
Origin of Genetics
RNA is likely first genetic material
multiple functions: encodes information (self-replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA)
makes inheritance possible
makes natural selection & evolution possible
Origin of Eukaryotes
endosymbiosis
Life is defined partly by two properties: accurate replication and metabolism. Neither property can exist without the other. Self–replicating molecules and a metabolism–like source of the building blocks must have appeared together. How did that happen?
The necessary conditions for life may have been met by protobionts, aggregates of abiotically produced molecules surrounded by a membrane or membrane–like structure. Protobionts exhibit some of the properties associated with life, including simple reproduction and metabolism, as well as the maintenance of an internal chemical environment different from that of their surroundings.
Laboratory experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds. For example, small membrane–bounded droplets called liposomes can form when lipids or other organic molecules are added to water.

42. Timeline Key events in evolutionary history of life on Earth
3.5–4.0 bya: life originated
2.7 bya: free O2 = photosynthetic bacteria
2 bya: first eukaryotes

43. Prokaryotic ancestor of eukaryotic cells
~2 bya
First Eukaryotes
Development of internal membranes
create internal micro-environments
advantage: specialization = increase efficiency
natural selection!
nuclear envelope
endoplasmic reticulum (ER)
plasma
membrane
infolding of the plasma membrane
nucleus
DNA
cell wall
plasma
membrane
Prokaryotic
cell
Prokaryotic ancestor of eukaryotic cells
Eukaryotic
cell

44. internal membrane system
1st Endosymbiosis
Evolution of eukaryotes
origin of mitochondria
engulfed aerobic bacteria, but did not digest them
mutually beneficial relationship
natural selection!
internal membrane system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion

45. photosynthetic bacterium chloroplast & mitochondrion
Eukaryotic
cell with
mitochondrion
2nd Endosymbiosis
Evolution of eukaryotes
origin of chloroplasts
engulfed photosynthetic bacteria, but did not digest them
mutually beneficial relationship
natural selection!
photosynthetic bacterium
chloroplast
mitochondrion
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion

46. Theory of Endosymbiosis
Lynn Margulis
Theory of Endosymbiosis
Evidence
structural
mitochondria & chloroplasts resemble bacterial structure
genetic
mitochondria & chloroplasts have their own circular DNA, like bacteria
functional
mitochondria & chloroplasts move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell

47. Cambrian explosion Diversification of Animals
within 10–20 million years most of the major phyla of animals appear in fossil record
543 mya