1. Evolution
Chapters 22, 23, 24, 25 and 26

2. Essence of Darwin’s Ideas
Natural selection
heritable variation exists in populations
over-production of offspring
more offspring than the environment can support
competition
for food, mates, nesting sites, escape predators
differential survival
successful traits = adaptations
differential reproduction
adaptations become more common in population

3. Evidence for Evolution
Paleontology – fossils show change in a species over time
Biogeography – Similar species are found in similar ecosystems around the world
Morphology – Comparing structures
Homologous structures – body parts with similar structure but possible different function. Shows common ancestry
Analogous structures – similar structure develops in organisms that share a common ecosystem but not a common ancestry
Biochemical or Molecular - Similarities in gene sequences, proteins, DNA

4. How old is that fossil? Relative Dating Absolute Dating
Age of fossils based according to their location in strata
Absolute Dating
Age of fossils determined by analyzing the content of radioactive isotopes found in the fossil.
Half-life: The length of time required for half of the radioactive elements to change into another stable element.

5. Layers of deposited sediment Younger stratum with more recent fossils
Figure 22.3 Formation of sedimentary strata with fossils
Older stratum
with older fossils

6. Homologous Structures

7. Analogous Structures

8. Comparative hemoglobin structure
Molecular Homology
The sequence in DNA & proteins is a molecular record of evolutionary relationships.
Why compare DNA & proteins across species? 10 20 30 40 50 60 70 80 90
100
110
120
Lamprey
Frog
Bird
Dog
Macaque
Human 32 8 45 67
125
Comparative hemoglobin structure
Molecular Record
What are we comparing here? - comparing DNA (base sequence) & proteins (amino acid sequence)
What assumption do we make about genes and relatedness?  the more closely related, the more DNA bases & amino acids you have in common
have to compare genes for protein the organisms have in common… can’t compare genes for proteins you don’t have
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans

9. Evolution evidence at the cellular level
Domains: Archaea, Bacteria and Eukarya
Elements conserved through all: DNA, RNA and many metabolic pathways.
Eukaryotes – core features:
Cytoskeleton
Nucleus
Membrane-bound organelles
Linear chromosomes
Endomembrane system

10. How do genetic variations occur?
What is Evolution?
Change in the genetic makeup of a population over time.
Fitness – those with favorable variations for survival and reproduction.
Populations can evolve, not individuals.
Diverse gene pool good for long-term survival of a species. Genetic variations are important!
How do genetic variations occur?

11. Where does Variation come from?
Mutation
random changes to DNA
errors in mitosis & meiosis
environmental damage
Sexual reproduction
mixing of alleles
genetic recombination
new arrangements of alleles in every offspring
new combinations = new phenotypes

12. 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

13. 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

14. 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

15. 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!

16. 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

17. 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

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

19. Practice Problem:
In a population of 100 cats, there are 16 white ones. White fur is recessive to black.
What are the frequencies of the genotypes?

20. 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 survive and reproduce better.

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

22. 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

23. Effects of Selection

24. 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

25. 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

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 population 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. 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.

33. 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

34. 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.

35. 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.

36. 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

37. 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.

38. 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

39. 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

40. 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

41. 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

42. 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

43. Overview: Investigating the Tree of Life
Phylogeny is the evolutionary history of a species or group of related species usually organized into a phylogenetic tree
Phylogenetic trees and cladograms (also tree shaped) seek to arrange organisms based on common ancestry

44. What is the difference between a phylogenetic tree and a cladogram?
In phylogenetic trees branch lengths can represent the amount of genetic change or are proportional to time
In cladograms the branch lengths are usually considered to be arbitrary
Phylogenetic tree – branch length based on relative genetic change in each lineage
Cladogram

45. What evidence are phylogenetic trees and cladograms based on?
Morphologies, genes, and biochemistry of living organisms
Organisms with similar morphologies or DNA sequences are likely to be more closely related
Must distinguish whether a similarity is the result of homology or analogy
Homology is similarity due to shared ancestry
Analogy is similarity due to convergent evolution (shark/dolphin)

46. What is evolution? Directions:
Use the color images I’ve provided to brainstorm what you know about how evolution works.
There are many interrelated concepts pertaining to evolution that could be associated with these images (shoot for 8-10).
Record your ideas on a separate sheet of scratch paper, they will serve as our basis for class discussion.

47. Homework 3/13 Finish evidence for evolution worksheet(s).
Complete section 5 (gel electrophoresis) of biotech packet.
Review evolution of populations in notes packet and in text book (Chapter 23, pages ).