• National Science Museum– Sue and Thai Dinosaurs Exhibition
– Evolution, species and speciation– Population genetics
5 6
2
7
Sue the Tyrannosaurus rex (67-65 MYA)8
Siamotyrannus isanensis (130 MYA)9Lucy the Australopithecus afarensis (3.2 MYA)
10
Cenozoic Era display in Natural History Museum11Bio-Geo Path at Mahidol, Payathai
12
3
13 14
Nothing makes sense in biology, except in the light of evolution.(T. Dobzhansky, 1973)
15
Mechanisms of Evolution
• Hawaiian Drosophila– 500 described
species– One fertilized female,
a single founder– More species than
islands• Island within island
– Keneshiro hypothesis• Mating behaviour
plays role in speciation.
Kenneth Kaneshiro, Evolutionary biologist 16
Introduction
• Darwin introduces a revolutionary theory– On the Origin of Species by Means of
Natural Selection (November 24, 1859)• Species are descendants of ancestral species• Natural selection as evolutionary process
17
Introduction
• Natural selection as evolutionary process– Population changes over time, certain
heritable traits can help organism leave offspring than other.
• Evolutionary adaptation– An accumulation of inherited characteristics that
enhance organisms’ ability to survive and reproduce in specific environment.
18
4
Introduction
• Evolution– Descent with modification– A change over time in the genetic
composition of a population• Speciation: new species
– A gradual appearance of all of biological diversity.
19 A marine iguana, well-suited to its rocky habitat in the Galapagos Islands. 20
Historical Context
• Darwinism– Timing and logic– Resistance to the idea of evolution
• Western culture: Earth is a few thousand years old, populated by unchanging organisms.
21
Scala Naturae
• The sacle of nature and classification of species– Aristotle (384-322 B.C.) →
• Scala naturae (scale of nature)
• (linear)
– Carolus Linnaeus (1707-1778) → • classify life’s diversity for the greater glory of
God.
• (nested)
22
The historical context of Darwin’s life and ideas.23
Catastrophism
• Fossils, Cuvier and catastrophism– Fossils
• Remains or traces of organisms from the past.
24
5
25
Catastrophism
• Fossils, Cuvier and catastrophism– Paleontology
• The study of fossils developed by Georges Cuvier (1769-1832)
• Catastrophism– Not believe in gradual evolution, strata boundaries
came from catastrophism.– Sudden and violent changes (flood or drought) that
can destropy many species.
26
Fossils from strata of sedimentary rock: The Colorado river and the Grand Canyon.27
Gradualism and Uniformitarianism
• Theories of Gradualism– Change can take place by the cumulative
effect of slow, but continuous process.
28
Gradualism and Uniformitarianism
• Uniformitarianism– James Hutton and Charles Lyell →
– Geological processes are operating today as in the past, at the same rate.
• Darwin thought that similar slow process could act on organism and produce changes as well.
29
Lamarck’s Theory of Evolution
• Jean-Baptiste de Lmarck– Evolutionary change explains the fossil record
and organisms’ adaptations to their environments.
• Changes occur, but no extinction. Species only transformed.
– How does evolution occur?• Use and disuse• Inheritance of acquired characteristics
– Innate drive
30
6
Acquired traits cannot be inherited: the bonsai.31
Darwin’s Research
• The Origin of Species– Species change through natural selection
• Darwin– Shrewsbury (western England)– University of Edinbrugh (medicine)– Cambridge University (clergyman)
• John Henslow (botanist)• Robert FitzRoy (captain of HMS Beagle)
32
The Voyage of the Beagle
• What did Darwin find?
– Various adaptation of plants and animals
– Ecological diversity, from grassland to high mountain
– South America temperate species are resembled species in the tropic, rather than Europe temperate species.
33
The Voyage of the Beagle
• What did Darwin find?
– Fossils were distinct, but resemble those living species of the continent.
– Geologic processes can change the landscape• Principles of Geology (Chales Lyell, 1830)
– Galapagos island species
34
The voyage of HMS Beagle
35 36
7
Darwin’s Focus on Adaptation
• Adaptation and speciation– Could a new species arise from an
ancestral form by the gradual accumulation of adaptations to a different environment?
• Galapagos finches– Their beaks and behaviours are adapted to specific
food found on their specific islands.
37
Darwin’s Focus on Adaptation
• The origin of species– 1840s
• major features done, Darwin was in poor health.
– 1844 • the long essay was written but unpublished.
– 1858 • Alfred Russel Wallace wrote to Darwin
– 1859 • Darwin published “The Origin of Species”
38
Beak variation in Galapagos finches
39
The Origin of Species
• Descent with modification– Darwin’s view of life– Tree of life
• Elephant evolution
– Linnaeus taxonomy• Reflect the branching history of the tree of life
as species descended from their common ancestors.
40
Descent w
ith modification: evolutionary tree of elephant
41 42
8
Observations and Inferences
• Observations• Population would increase exponentially if all
individual reproduced successfully. (after Thomas Malthus, 1798)
• But, populations tend to remain stable.• Resources are limited
43
Observations and Inferences
• Inference– Only a fraction survive as many struggled
for existence.• Members of species vary• Much of variations can be inherited (artificial
selection in agriculture)
44
Observations and Inferences
• Inference– Some traits give more fitness to organism
(survive and reproduce)– Unequal fitness lead to gradual change in
a population.
45 Overproduction of offspring 46
Variation in population
47
Artificail selection48
9
Natural Selection
• Definition– Natural selection is the differential
success in reproduction that results from the interaction between individuals that vary in heritable traits and their environment.
• Differential success in reproduction– The unequal ability of individuals to survive and
reproduce.
49
Natural Selection
• Effects– Over time, natural selection can increase
the adaptation of organisms to their environment.
• If the environment change or individual move to new habitat, natural selection could sometimes give rise to new species.
50
Camouflage as an example of evolutionary adaptation
51
Natural Selection
• Unit of evolution– A population is the smallest unit that can
evolve.• Natural selection occurs through interaction
between individual and environment, but individual do not evolve.
• Population– A group of interbreeding individuals belonging to a
particular species and sharing a common geographic area.
52
Natural Selection
• Measuring evolution– Relative proportions of heritable variations
in a population over a succession of generations.
53
Natural Selection
• Life as Darwin see it– Life evolve through gradual accumulation
of small changes.• Natural selection operates in various contexts
over time as can be seen in geological evidence and the entire diversity of life.
54
10
Differential Predation and Guppy Population
• Guppies ( Poecilia reticulata)– Observation
• Different average age and size at sexual maturity.
• Correlation with type of active predator.– Small killifish → prey on juvenile guppies– Pike-cichlid fish → prey on mature guppies
» Guppies with pike-cichlid reproduce at younger age and are smaller at maturity.
55
Differential Predation and Guppy Population
• Guppies ( Poecilia reticulata)– Experimentation
• Transplantation experiment– Move guppies from pike-cichlid pool to killifish po ol
(has no guppy prior the experiment)
56
57 58
59
The Evolution of Drug-Resistant HIV
• Human Immunodeficiency Virus (HIV)– The drug 3TC interfere with reverse
transcriptase. 3TC is cytosine analog.– Some virus has reverse transcriptase that
can distinguish 3TC and normal C.• This variation replicate slower than normal
virus.• With 3TC, this variant replicate bettern than
normal virus.
60
11
The Evolution of Drug-Resistant HIV
• Human Immunodeficiency Virus (HIV)– Drug-resistant pathogen can spread
quickly in the present of strong selective force.
61
Natural Selection
• Two key points– Natural selection is a process of edition
not creation.– Natural selection depends on time and
place.• Adaptive in one situation become maladaptive
in other situations.
62
Evolution of drug resistance in HIV.63
Evidence of Evolution
• Evolution can help answer questions– Why certain characteristics in related species
have an underlying similarity even though they may have very different function.
• Homology– Anatomical homologies
• Comparative embryology
– Molecular homologies
• Biogeography• The fossil record
64
Homology
• Homology– Similarity resulting from common
ancestry.– Anatomical homologies (comparative
anatomy)• Comparison of body structures between
species.
65
Homology
• Homology• Homologous structure
– Variation on a structural theme that was present in their common ancestor.
– Vestigial organs» Remnants of structures that served important
functions in the organism’s ancestors.
• Comparative embryology– The comparison of early stages of animal
development, not visible in adult organisms.
66
12
Homology
• Homology– Molecular homologies
• Similarity at the molecular level. All forms of life use the same genetic machinery of DNA and RNA.
• Many share genes (bacteria vs human)– Homologies and the tree of life
• Molecular homology can date back to the ancestral past.
• Some homologies evolved just recently (tetrapods), 5-digit limbs → nested pattern.
• Organisms evolved from a common ancestor.67
Mammalian forelimbs: homologous structure68
Anatomical similarities in vertebrate embryos
69 Comparision of a protein found in diverse vertebrates 70
71
Biogeography
• Biogeography– The geographic distribution of species.
• Closely related species tend to be found in the same geographic region.
• Distant region with same ecological niche occupied by different species (sometimes look similar).
72
13
Biogeography
• Biogeography• Australia
– Australian marsupials have eutherian lookalike. (i. e. sugar glider and flying squirrel).
– Convergent evolution (not homologous)
• Endemic– Species that found no where else (Galapagos,
Hawaii)
73
Different geographic regions, different mammalian brands
74
The Fossil Record
• The fossil record– The Darwinian view of life predicts that
evolutionary transitions should leave signs in the fossil record.
• Ape and Human fossils• Dinosaur and bird fossils• Terrestrail mammal and whale fossils• Not so fossil: prokaryote and eukaryote
75 76
77
A transitional fossil linking past and present
78
14
Darwin’s Theory of Evolution
• It can explains so many different kinds of observations.– Homologies match patterns in space
(biogeography) and time (the fossil record).
– Natural selection can explain how similar adaptations can evolve independently (convergent evolution, e.g. sugar glider and flying squirrels)
79
Fact or Theory?
• Does Darwinian view of lfie a fact or a theory?– As can be seen from various evidence, it is a fact.
• The different between theory and fact or hypothesis.– With many observation and data, hypothesis
become theory.
• Is natural selection the only evolutionary mechansim?– No. Other factors have been found to play
important roles. 80
The Origin of Species
The definition of species and speciation process
Outline
• Key concepts– Biological species concept– Reproductive isolation– Speciation
• Allopatric speciation• Sympatric speciation
– Macroevolution and many speciation events
82
Mystery of Mysteries
• Darwin’s diary– Galápagos Island
• “Both in space and time, we seem to be brought somewhat near to that great fact – that mystery of mysteries – the first appearance of new beings on this earth.”
• Speciation– The origin of new species– The source of biological diversity (species
diversity)
83
Mystery of Mysteries
• Evolutionary changes–Microevolution
• Changes confined to single gene pool (at species level)
–Macroevolution• Evolutionary changes above species
level– Evolutionary novelties (e.g. feathers
separate birds from dinosaurs)
84
15
The flightless cormorant (Nannopterum harrisi), one of many new species that have originated on the isolated Galápagos Islands.
How would you explain the origin of flightless birds?
85
Two patterns of evolutionary change
86
Patterns of Evolutionary Changes
• Anagenesis– Ana=new, genos=race (new race)– One species transform to another species.– Number of species not increase
• Cladogenesis– Klados=branch, genos=race (branching evolution)– Gene pool split, give rise to one or more new
species– Number of species increase
• Biological diversity– Cladogenesis
87
What is Species?
• Species– Latin word, species=kind or appearance
• Real or artificial?– Real entity as species can recognize its
own species.– Higher taxonomic levels are artificial.
• Continuous or discrete– Discrete (morphologically distinct species)
88
The Biological Species Concept
• Biological species concept (BSC)– Ernst Mayr (1942)– Members of the same species are
reproductively compatible.• A species as a population or group of
populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce fertile offspring with other populations.
89
The Biological Species Concept
• Limitations of the BSC– Fossil (extinct species)– Asexual organisms– No information of reproduction =
inconclusive– Has no potential to interbreed
(geographically isolated)
90
16
Similarity between different species
Diversity within a species
(Left) The eastern meadowlark (Sturnella magna)
(Right) The western meadowlark (Sturnella neglecta)
Both are distinct species, their song and behaviour are different prevent interbreeding if they meet in the wild.
All human (Homo sapiens) can interbreed.
91
Reproductive Isolation
• Reproductive isolation• Factors that prevent members of two
species producing viable, fertile hybrid offspring.
– Many barriers can work together.– Gene flow restriction
92
Reproductive Isolation
– Prezygotic barriers (before the hybrid zygotes are formed)
• How can reproductive barriers (reduction in gene flow) between sympatric populations evolve when members remain in contact?
– Chromosomal mutation » Polyploidy
– Nonrandom mating» Habitat differentiation» Sexual selection
115
Polyploidy
• Polyploidy– Mutation that increase extra set of
chromosomes.– Rare in animals, but more common in
plants.
• Autoploidy– Extra set of chromosome originate from a
single species (Greek: autos=self)
116
Polyploidy
• Mechanism – Nondisjunction in cell division (2n →4n)
• Results– 2nx4n→3n which is sterile– 4n can self and mate with other 4n– In ONE generation, autoploidy generates
isolation without any geographic barrier.
117
Sympatric speciation by autopolyploidy in plants
118
Sympatric Speciation
• Allopolyploid– Greek allos=other– Mechanism
• When 2 species interbreed and produce sterile hybrids → this hybrid can asexually reproduce
• Or, with some events, allopolyploid will emerge (see figure)
119
Sympatric Speciation
• Allopolyploid– Result
• Allopolyploid that can interbreed with each other, but not with its both parent species.
• Allopolyploid plant represents a new biological species.
• Speciation without geographic barrier.
120
21
One mechanism for allopolyploid speciation in plants
121 122
123
Sympatric Speciation
• Polyploid species– The goatbeard plants
(genus Tragopogon)• Diploid species
– T. dubius, T. pratensis and T. porrifolius
• Tetraploid species– T miscellus (T. dubiusxT.
pratensis)
• Allopolyploid species– T mirus (T. dubiusxT.porrifolius)– With ongoing hybridization with
its parent species.
http://ftp.funet.fi
124
Sympatric Speciation• Agricultural crops are polyploid
– Oats, cotton, potatoes, tobacco and wheat
– The bread wheat ( Triticum aestivum)
• Allohexaploid – Six sets of chromosomes, two
sets from 3 different species– First polyploid might occur
naturally in the Middle East, approximately 8,000 years ago.
– Breeding program can be used to create allopolyploid species.
• Chemical can be used to induce meiotic and mitotic errors.
http://www.littletree.com.au/bread.htm125/239 126
22
127
Sympatric Speciation
• Habitat Differentiation and Sexual Selection– The North American apple maggot fly
(Rhagoletis pmonella)• Reproductive isolation occurs as
subpopulation prefer different food than parent population (native hawthorn trees).
128
http://www.pbase.com/crocodile/image/32253695 129
Sympatric Speciation
• The lake Victoria– Only 12,000 years old, but there are 500
species of cichlid fishes. Similar genetically, suggested that they diverged just recently, probably from food preferences.
130
Sympatric Speciation
• Pundamilia pundamilia and P. nyererei– Sexual selection → females select males
from appearance.– Nonrandom mating, but pollution is
clouding the water.
131
Does sexual selection in cichlids result in reproductive isolation?
Males and females of Pundamilia pundamilia and P. nyererei
Under monochromatic orange light, females of both species mate indiscriminately resulting in hybrid and viable hybrids.
Under normal light, females of both species mate with male of the same species.
Mate choice based on male colouration by females is reproductive barrier. As prezygotic become breached in the lab it suggests that genetic different is small and the speciation occur just recently. 132
23
Adaptive Radiation
• Adaptive radiation– Evolution of many diverse species
• In new environment with many ecological niches to occupy.
• Same habitat, but after mass extinction (just what thought to happen 65 MYA, when dinosaurs gave way to mammals to diversify.
– Hawaii archipelago– Australia
133Long-distance dispersal: seeds of Pisonia plant on black noddy tern and Velcro invention.
Seeds
134
Adaptive radiation of the silversword alliance came from only one species of tarweed about 5 million years ago (molecular analysis).
Dubautia waialealae
Dubautia laxa
Dubautia linearis
Argyroxiphium sandwicense
Dubautia scabra
135
The Genetic of Speciation
• The monkey flowers ( Mimulus lewisiiand M. cardinalis)– Mechanism
(Darwin)– Little changes accumulate over time.– Species continuously adapted to the
environment.• Real evidence or just incomplete data?
– Not all of the changes can be fossilized (physiological or biochemical changes)
140
The Tempo of Speciation
• Punctuated equilibrium– Niles Eldredge and Stephen Jay Gould– Long stasis, punctuated by sudden
change.• Real evidence or just incomplete data?
– Incomplete fossil data set appears to be punctuated .
• Both tempo is possible.
141
Two models for the tempo of speciation
Gradualism model
Punctuated equilibrium model
142
Macroevolution
• Macroevolution– Evolutionary changes above species
levels.– As small differences accumulated, it would
become clear and more pronounced.
143
Macroevolution
• Evolutionary novelties–Descent with modification
• Complex structure evolved from something thing with same basic function.
– How would human eyes have evolved in gradual increments?
– How would simple eyes be any use to the ancestors?
» Only complicate eyes are useful? Certainly not.
144
25
Macroevolution
• Evolutionary novelties–Exaptation
• Structures that evolve for one thing, but have another function sometime later (feather and flying).
145
A range of eye complexity among molluscs
Patch of pigmented cells in limpet (mollusc)
Eyecup in another mollusc
Pinhole camera-type eye (no lens) in Nautilus (mollusc)
Eye with primitive lens (transparent epithelium) in Murex (mollusc)
Complex camera-type eye in squid (mollusc), similar to vertebrate eyes,
but evolve independently 146
Evolution and Development
• Genes that control development– How slight genetic divergences can be
magnified into major differences between species?
• Genes that control development: rate, timing and spatial patterns; from zygote to adult.
– Heterochrony• Greek: hetero=different + chronos=time• Change in rate and timing of development
events.
147
Evolution and Development
• Genes that control development– Allometric growth
• Greek: allos=other + metron=measure• Different growth rate and pattern during
development alters body proportions.– Human body and limbs– Human and chimp skulls– Salamander feet
148
Allometric growth
Differential growth rates in human.Legs and arms lengthen more than head and trunk.
Comparison of chimpanzee and human skull growth.
Similar for both chimpanzee and human in fetus.
In adult, human skull become rounded with little sloping whereas chimp skull become elongated wilth sloping face.
149
Heterochrony
Salamanders that live on tree have their digit development end sooner, giving more webbing to developed for tree climbing.
Short, but more webbing
Different
Time
150
26
Paedomorphosis – retaining larval characteristics even in adult form (full size, sexually mature).
151
Different regions of Hox genes expression in chicken and fish.
Homeotic genes
Changes in Spatial Pattern
Determine where basic structures (a pair of wings or legs) will develop.
152
Hox mutations and the origin of vertebrates
Invertebrate with one copy of Hox complex
First duplication occurred 520 MYA
New set of genes with new role of backbone development.
Second duplication 425 MYA yielding 4 set of Hox complexes made jaws and limbs development possible.
153
Yellow line indicates the evolution of modern horse with trend toward increasing size, reduced number of toes and grazing adaptations.
Grazers
Browsers
Evolution is not goal-oriented. 154
Population Genetics
The study of allele frequencies dynamic in a population.
Modern Synthesis
• The modern synthesis– Darwin
• Quantitative characters (continuous) → multiple genes with Mendelian inhertitance
– Mendel • “Either or” (red or white flower)
– Modern synthesis• Integrated theory of evolution from Darwin,
Mendel and mathematics.
156
27
Modern Synthesis
• The modern synthesis
– R.A. Fisher (1890-1962)
– J.B.S. Haldane (1892-1975)
– Sewall Wright (1889-1988) a geneticist
157
Modern Synthesis
• The modern synthesis
– Theodosius Dobzhansky (1900-1975) a geneticist
– Ernst Mayr (1904-2005) a biogeographer
– George Gaylord Simpson (1902-1984) a paleontologist
– George Ledyard Stebbins (1906-2000) a botanist
158
Sir Ronald Aylmer Fisher John Burdon Sanderson Haldane
Sewall Green Wright
Ernst Mayr Theodosius DobzhanskyGeorge Gaylord Simpson
George Ledyard Stebbins
159
Introduction
• Population genetics– The study of allele frequency distribution
at the population level.
– Gene pool• All the genes present in breeding population at
a given period.
– Allele frequency• Proportion of a given allele to the total allele of
that locus in a population.
160
Allele Frequency
• Allele– Alternate version of a gene at a given
locus on a chromosome.
– Diploid organism• There are two alleles on the homologous locus
on each chromosome.– There could be more than two alleles as well, calle d
multiple alleles (i.e. ABO bloodtype; IA, IB and i).
161
Allele Frequency
• Allele frequency (gene frequency)– For diploid organism, there are two alleles
(A or a) at a locus on homologous chromosomes.
• Frequency of allele A is p.• Frequency of allele a is q.
162
28
Total Alleles
• Total alleles– At a particular time, a total of all genes in
the population is called gene pool.• The total alleles at a locus is 2N in diploid
organism because there are two set of chromosomes in the nucleus.
– However, in Y-linked genes, there is only 1 Y-chromosome per nucleus. Eventhough the organism is diploid, there is only one copy of Y-linked gene in the cell.
» The total of alleles on any loci on Y-chormosome is only N.
163
Randomly Pick a Gamete
• Probability– Probability of getting gamete containing
allele A is p.
– Probability of getting gamete containing allele a is q.
• The probability of getting either gamete containing allele (A) or (a) is p+q=1.
164
Fertilization of Gametes
• Fertilization of gametes– Zygote = fertilization of 2 gametes.
• Probability of getting one gamete containing allele (A) and another gamete containing allele (A) is pxp = p 2.
• Probability of getting one gamete containing allele (a) and another gamete containing allele (a) is qxq = q 2.
165
Random Zygote
• Zygote– After fertilization of two gametes, one from male
and another from female.
• Probability of getting zygote (AA) is pxp = p 2.• Probability of getting zygote (aa) is qxq = q 2.
• Proability of getting zygote (Aa) is pxq = pq.• Proability of getting zygote (aA) is qxp =qp.• Probability of getting heterozygotes (Aa) or (aA) i s pq+qp
= 2pq.
166
Total Possible Zygotes
• Total possible zygotes– Homozygous zygotes (AA) or (aa) is p 2 or
q2.– Heterozygous zygotes (Aa) is 2pq.
• Probability of getting zygotes (AA) or (aa) or (Aa) is p 2+2pq+q 2=1
167
Allele and Genotype Frequencies
• Allele frequency– p+q = 1
• Genotype frequency– p2+2pq+q 2 = 1
• Binomial expansion– (p+q) 2 = p2+2pq+q 2 = 1
168
29
Genotypic and Allelic Frequencies
Heterozygote frequency will be at maximum in a diplo id two-allelic population when allelic frequencies p a nd q are equal at 0.5.
169
Polyploidy
• Haploid– (p+q) 1 = p+q = 1
• Diploid– (p+q) 2 = p2+2pq+q 2 = 1
• Triploid– (p+q) 3 = p3+3p2q+3pq 2+q3 = 1
• Tetraploid– (p+q) 4 = p4+4p3q+6p2q2+4pq3+q4 = 1
170
Pascal’s Triangle
11 1
1 2 11 3 3 1
1 4 6 4 11 5 10 10 5 1
1 6 15 20 15 6 11 7 21 35 35 21 7 1
1 8 28 56 70 56 28 8 1
012345678
n =
171
Multiple Alleles
• Multiple alleles– There are more than two alleles at a gene
locus.• Example: ABO bloodtype
– Three alleles I A, IB, and i– Allele frequencies p, q, and r
and reproduction) will leave more offspring than less fit.
199
Natural Selection
• On HWE– Differences in survial and reproductive
success would disturb HWE.• Red flowers (CRCR)
– would produce more offspring (set more seeds) as they attract more pollinators.
» Frequency of C R would increase whereas CW decline.
200
Genetic Drift
• Genetic drift– Fluctuation of allele frequency from
generation to generation.
– Drift tend to reduce genetic variation, lead to fixation of genes.
– Small population is the most affected by drift.
201
Genetic Drift
• The bottleneck effect–A population is forced through a
restrictive “bottleneck” such as disasters (storm, flood, drought). • Gene pool of this surviving population
would be different from the original.
202
Genetic Drift
• The founder effect– A small population (or even one fertilised
female) becomes isolated from its large population, and establish new population, possibly in the new location.
• Isolation bottleneck
203 204
35
205 206
207
Gene Flow
• Gene flow– Movement of the gene from one population
to another.• Movement of individuals for animals, or plants’
seeds• Movement of gametes for plants as in pollen
via pollinators
208
Gene Flow
• On HWE,– Immigration and emigration would
increase or decrease allele frequencies in populations.
209 210
36
211
Adaptive Evolution
• Adaptation– Something that increase fitness of the organisms,
compared to those that don’t.
• Adaptive evolution– Evolution that occurs to increase fitness of the
organisms.• Adaptive traits• Maladaptive traits
• Natural selection– Only natural selection can lead to adaptation.
212
Genetic Variation
• Genetic Variation– Variation within a population
• Polymorphism ( as oppose to monomorphic )– More than one morph can be detected (>0.01)
» Phenotypic polymorphism» Genetic polymorphism
• Measuring genetic variation– Average heterozygosity (e.g. it is 14% in Drosophila)
» Of all its 13,000 loci → 1,800 loci are heterozygous.
213
Genetic Variation
• Genetic Variation– Variation between populations
• Geographic variation– Cline = a graded change in trait along a geograhpic
axis.
214
Nonheritable variation within a populationEuropean map butterflies (Araschnia levana) have 2 seasonal forms. If one of these form have better fitness, there would be no change in colouration alleles as they are identical genetically.
215
Geographic variation in chromosomal mutations
Fusion of chromosomes (2.4 is between chromosome 2 and chromosome 4)
This fusion appear to be neutral.
These two patterns (yellow vs red dots) are different.
216
37
217
Does geographic variation in yarrow plants (Achillea) have a genetic component?
Collecting seeds to grow in the common garden (same elevation). Plants’ height reflect both genetic variation and environmental effects.
cline
218
Fitness
• Fitness– How well the organism survive and
reproduce.• The contribution an individual makes to the
pool of the next generation, relative to the constribution of other individuals.
– Relative fitness• The contribution of a genotype to the next
generation compared to the contributions of alternative genotypes for the same locus.
– Range from 1 to 0.219
Fitness
• Fitness• Inclusive fitness
– Inclusive fitness = direct fitness + indirect fitne ss
220
Mode of Selection
• Mode of selection–Natural selection can alter
phenotypic distribution in 3 ways.• Directional selection
– Selection that deviate from average to one of the directions. (fossil bears)
221
Mode of Selection
• Disruptive selection– Selection that favour extreme traits, but
against intermediate traits. This mode could lead to speciation. (finch’s beak)
• Stabilizing selection– Selection that favours intermediate traits,
but against extreme traits. This mode reduces variation. (human birth weight)
222
38
223 224
225 226
227 228
39
The Preservation of Genetic Variation
• Why recessive alleles remain in the population?– Diplody
• Dominant alleles conceal recessive alleles in heterozygote.
Using a virtual population to study the effects of selection
Blue jay recieves a food reward it can peck a screen with virtual moths.
Generation time
Phenotypic variation
Frequency independent selection
Patterned digital moths are harder to detect
234
40
Evolution of Sex
• Evolution of sex–How did sex evolve in the first place?–To increase population expansion?
(asexual is better)• Reproductive handicap of sex
– Asexual population increase rapidly compared to sexual population (assuming that 2 surviving offspring per female).
235
Evolution of Sex
• Evolution of sex–Majority of eukaryotes reproduce
sexually.–What advantage does sex provide?
• Despite sex’s reproductive drawback, sexual reproduction is favoured by natural selection because sex generates genetic variations enable future adaptation to ever-changing environment.
236
Evolution of Sex
• Evolution of sex• Coevolution between species and
its pathogen–(Red Queen race : Alice to run as fast
as she could just to stay in the same place)
237 Sexual dimorhism and sexual selecion in peacocks and peahens. 238
The reproductive handicap of sex
239
Perfect Oranism
• Why could natural selection not create “perfect organism”?– Evolution is limited by historical
constraints.– Adaptations are often compromises.– Chance and natural selection interact.– Selection can only edit existing variations.
240
41
Perfect Oranism
• Better than…– Natural selection can select better trait,
compared to other
241
References
• Textbooks– Campbell, N. A. (2008). Biology. San
Francisco, Pearson Benjamin Cummings. – Starr, C. (2006), Basic Concepts in Biology
