Transcript Evolution

Evolution
Content
• 1. An introduction
•
•
•
•
•
•
to evolution
2. Historical view (the evolutionary
thinking)
3. Genetic variation
4. Mechanisms: the processes of evolution
5. Microevolution vs Macroevolution
6. Speciation
7. Issues on evolution
Evolution
 Evolution = Change.
 Biological Evolution = Change in
the intrinsic qualities of life over
time.
 NOT progressive change.
 What can change?
Characteristics of species
Number of species
Evolution
 Microevolution = Change in the
genetic qualities of populations
within a species over time.
 Macroevolution = Change in the
number of species and the
formation of groups of species.
 Speciation = formation of species
Results of Evolution
• Anagenesis = change within a species
lineage(number not increase)
• Cladogenesis = change and
diversification
History: Early 1800’s
 Natural Theology
Discover God’s plan, study nature.
 Essentialism = Organisms are
imperfect reflections of perfect
eternal “essences.” (invariant)
 Natural groups reflect the
essential groups in the mind of
God.
History: Early 1800’s
 Paleontology = study of fossils.
 Fossil = preserved remnant of an
organism that lived in the past
Certain fossils only found in certain
rock strata (layers).
Some organisms are extinct!
 Earth = VERY OLD
 Sedimentary Rocks = layered rocks
formed by settling particles.
Sedimentary Rocks & Fossils
youngest layer
oldest layer
Sedimentary Rocks & Fossils
Dead Thing
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks & Fossils
EROSION
Fossil (Dead Thing)
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks
Geologic Time Scale
 Geologic scale based on the fossil
record. (time divisions UNequal)
 Eras = four largest time periods
(Precambrian --> Paleozoic -->
Mesozoic --> Cenozoic)
 Periods subdivide eras.
 Mass Extinction = extinction of a
large proportion of existing species.
They separate many eras or periods.
Geologic Time Scale
Cenozoic
Mesozoic
extinction of dinosaurs
first flowering plants
first dinosaurs & mammals
Paleozoic
“fern” forests form coal
first land plants & animals
first vertebrates
near present oxygen levels
Precambrian
Eons = hundreds of
millions of years in
duration(บรมยุค)
Eras(มหายุค)
Eons
period(ยุค)
epochs.
Biostratigraphy: The
organisation of sedimentary
rocks into units on the basis
of the fossils they contain
Biostratigraphy:
Charles Darwin
Mid-1800’s, Charles Darwin
 Studied medicine & theology
 Traveled on H. M. S. Beagle
 Bred pigeons
The Origin of Species, 1859
 TWO big ideas
Common Descent (old idea)
Natural Selection (new idea)
Natural Selection
 Mechanism of change
within one species.
(Proposed by Darwin.)
 Microevolutionary
process.
 First evidence from plant
and animal breeding by
humans
to create domestic forms.
Natural Selection
 Populations can grow tremendously.
 In nature, populations remain stable in
size due to limited resources (K).
 THEREFORE, there is a struggle to
survive and reproduce within species.
 Organisms vary in inheritable
characteristics (genetic).
 THEREFORE, reproduction varies
based on differences in inherited traits.
Natural Selection
DEFINITION
Differential reproduction
(survival) based on
differences in inherited
characteristics.
NOT “survival of the fittest”
Population
Population
Population
Population
Population
Population
Population
Fitness
 FITNESS = the relative contribution
of an individual to the next
generation
 More fit = more surviving offspring
 Less fit = fewer surviving offspring
 “Survival of the fittest” = circular, non
biological statement
แฟคเตอร์ที่มีอิทธิพลต่อ fitness
Adaptation
 Adaptation = characteristic that
results from natural selection also...
a trait that enhances the
reproductive success of the bearer.
 Not ALL characteristics of
organisms are “adaptations.”
 Difficult to provide evidence that a
characteristic is truly an adaptation.
Laboratory Selection
ลายจุดบนตัวปลาหางนกยูงส่ วนใหญ่ ถูก
ควบคุมด้ วยพันธุกรรม ลายจุดนีช้ ่ วยใน
การพรางตัวให้ เข้ ากับสิ่ งรอบข้ างเพื่อ
ป้ องกันการถูกจับกินโดยปลาใหญ่ แต่
ลายจุดนีก้ ช็ ่ วยให้ ดูเด่ นกว่ าตัวที่ไม่ มลี าย
จุด จึงดึงดูดคู่ผสมพันธุ์
Microevolution
Sexual Selection
“Special” Kinds of Selection
 Natural Selection = differential
reproduction (survival) based on
differences in inheritable
characteristics (different alleles).
 Sexual Selection = natural
selection based on mate choice.
 Artificial Selection = natural
selection due to conscious human
choice. (e.g., dogs, wheat)
Sexual Selection
Artificial Selection
Artificial Selection
p. 399
Population Genetics
 Population = localized group of
individuals of the same species
 Population genetics = studies the
genetic variation within populations
 Genotype = the genes (alleles)
possessed by an organism
 Phenotype = the physical
characteristics of an organism
Genetics “Review”
 Genes (DNA) in cells direct cell
activities.
 Most cells have TWO copies of
every gene. (DIPLOID)
 One copy from each parent.
 Sperm or egg have ONE copy of
every gene. (HAPLOID)
Genetics “Review”
Genetics “Review”
 The same gene can have different
forms (Alleles).
E.g., blue iris allele and brown iris
allele of eye color gene
 Diploid individual with the same 2
alleles = homozygote.
 Diploid individual with 2 different
alleles = heterozygote.
Genetics
 Gene “A” has 2 alleles,
“A” and “a.”
 AA or aa = homozygotes.
 Aa = heterozygotes.
 AA, Aa, and aa = genotypes.
 Calculation of allele frequencies.
Population Genetics
 Gene pool = all the alleles in a
population
 Genetic structure = frequencies
(%) of alleles and genotypes in a
population.
 Mendelian population =
interbreeding group within a
population.
Hardy Weinberg
 Hardy-Weinberg Theorem =
describes a population that is NOT
evolving.
p2 + 2pq + q2 = 1
p = frequency of A in the pop.
q = frequency of a in the pop.
p+q=1
Random mating
P(A)=p
P(a)=q
P(A)=p
P(a)=q
AA=p2
Aa =pq
aA=pq
aa=q2
AA + 2Aa + aa = p2 + 2pq + q2 = 1
(p+q) 2 = 1
p+q = 1
Hardy Weinberg
p2 + 2pq + q2 = 1
p2 = frequency of AA in the pop.
2pq = frequency of Aa in the pop.
q2 = frequency of aa in the pop.
Hardy-Weinberg
p2 + 2pq + q2 = 1
The frequency of AA in a population
at H.-W. equilibrium is
0.25.
What is the frequency of Aa in this
population?
Hardy-Weinberg
p2 + 2pq + q2 = 1
p2 = 0.25
p = 0.5
p+q=1
0.5 + q = 1
q = 0.5
Hardy-Weinberg
p2 + 2pq + q2 = 1
p = 0.5
q = 0.5
2pq = frequency of Aa
2(0.5)(0.5) = frequency of Aa
0.5 = frequency of Aa
Microevolutionary Processes
 Microevolution = small
scale evolutionary
changes.
 Natural Selection
 Non-random mating
 Genetic Drift
 Gene Flow (Migration)
 Mutation
Mutation
 Mutation = introduction of random
genetic variation. Source of new
alleles.
 THE SOURCE of variation.
 Change in the DNA (in a sex cell).
 Relatively rare and random.
 Some chemicals can increase
mutation rate (mutagens).
ผลกระทบของมิวเทชัน
• มิวเทชันอาจเกิดขึ้นที่ยนี ต่างๆที่ทาหน้าที่ควบคุม(regulatory
genes) ซึ่งมีผลกระทบค่อนข้างรุ นแรง เพราะยีนที่ทาหน้าที่ควบคุม
อาจมีอิทธิพลต่อยีนอื่นๆหลายยีน
• มิวเทชันที่ยนี ควบคุมส่ วนใหญ่จึงทาให้ไซโกตตาย ตัวอย่างของ
nonlethal regulatory mutations ที่เกิดกับ HOX
genes ในมนุษย์ซ่ ึงอาจก่อเป็ นผลให้เกิดลักษณะ polydactyly
ซึ่งหากให้ผลดีกจ็ ะกระจายไปในประชากร
Gene Flow
 Gene flow = Gaining alleles from or
losing alleles to another population.
Fertile individuals (emigration &
immigration)
Seeds
Pollen
Gametes
Genetic Drift
 Changes in the gene
pool of a (small)
population due to
chance.
 Chance =
random catastrophes
random individuals
begin a pop.
genes randomly passed
on to offspring
Genetic Drift
Genetic Drift
Genetic Drift
Genetic Drift
Genetic Drift
 Population Bottleneck = genetic drift
in small remnant population that later
becomes larger.
 Result: a large genetically similar population
 Founder effect = genetic drift in small
founding population that later
becomes larger.
 Example: polydactyly in the Amish
Population Bottleneck
p. 403
Population Bottleneck
No Genetic
Variation
Genetic
Variation
Small
Population
Much
Genetic
Drift
#
Large
Population
time
Large
Population
Cheetahs
Founder Effect
No Genetic
Variation
#
time
Genetic
Variation
#
time
Zoo Animals
Nonrandom Mating
 Assortative Mating = preferentially
mating with either similar or different
genotypes.
 Inbreeding = reproducing with
relatives; increases homozygosity.
(More likely to get 2 copies of the same bad
gene. INCEST TABOO)
 Outbreeding = reproducing with nonrelatives; increases heterozygosity.
Natural Selection
 Phenotype can be determined by a
single gene or by many genes.
 Stabilizing selection = removes
extremes.
 Directional selection = Removes ONE
extreme.
 Disruptive selection = Removes
intermediates; favors extremes.
Quantitative Characters
One Gene Characteristic
#
Many Gene Characteristic
#
Directional Selection
#
p. 405
Distribution
#
p. 405
Directional selection
• เกิดขึ้นเมือแอลลีลหนึ่งมี fitness
เหนือแอลลีลอื่นๆ กระบวนการนี้
จะเกิดไปจนกว่าแอลลีลจะฟิ กส์
และประชากรทั้งหมดแสดงฟี โน
ไทป์ ที่มีความเหมาะสมนั้น
• ตัวอย่าง เช่น ความต้านทานต่อ
ปฏิชีวนะ
Stabilizing Selection
#
p. 405
Distribution
#
p. 405
Disruptive Selection
#
p. 405
Microevolution
 Mutation - source of new variation
 Gene Flow - redistributes variation
 Genetic Drift - reduces variation (by
chance)
 Non-random mating - maintains
(outbreeding)
or reduces (inbreeding) variation
 Natural Selection - reduces variation
(due to environment)
Hardy-Weinberg Assumptions
NO EVOLUTION
 no mutation
 population is genetically isolated
 very large population size
 random mating
 no natural selection
Hardy-Weinberg
 Are the assumptions of HardyWeinberg likely to be met?
Nope.
 Why is the equation useful?
 Modification by terms for pop. size,
selection, non-random mating, etc.
more realistically model real
populations.
Hardy-Weinberg Assumptions
EVOLUTION
 mutation
 gene flow
 genetic drift
 assortative mating
 natural selection
Decreasing Variation
 Genetic Drift - reduces variation (by
chance)
 Inbreeding - reduces variation by
increasing homozygosity
 Natural Selection - reduces variation
(due to environment); disadvantaged
alleles disappear
Maintaining Variation
 Mutation - creates new alleles
 Neutral Alleles - do not affect the
fitness of an organism; are not
removed by natural selection
 Subpopulations - selection different in
different areas but gene flow keeps
them “mixing”
Dislocation of European bison's
subpopulations in Ukraine
Maintaining Variation
 Gene Flow through Sexual
Reproduction - new combinations of
alleles
 Polymorphism - two genotypes favored
by selection (often frequency dependent)
e.g., right mouthed & left mouthed scale eating fishes
 Heterozygote Advantage heterozygote parents produce some
homozygote offspring
Right mouthed & Left
mouthed scale eating fishes
conspicuously
asymmetrical left-bending
(left) and right-bending
(right) individuals of the
scale-eating cichlid fish
Perissodus microlepis
from Lake Tanganyika.
(Photo courtesy of A Meyer.)
Palmer Journal of Biology
2010
9:11 doi:10.1186/jbiol218
Sickle Cell Disease
 HbnHbn = “normal” red blood cells; no
sickle cell disease
 HbnHbs = some sickled red blood cells
some normal; mild sickle cell disease
and some protection from malaria
 HbsHbs = sickled red blood cells;
sickle cell disease causing death and
some protection from malaria
Sickle Cell Disease
 In malarial areas:
sickle cell
malaria
HbnHbn
none
highly susceptible
HbnHbs
mild
low susceptibility
HbsHbs
death
low susceptibility
Relationship of Phenotype and
Genotype
The Genotype codes for the Phenotype
-Almost
all
enzymes
are
proteins.
-Almost
all traits
are
produced
by the
action of
proteins.
Genotype  Phenotype
 Genotype and phenotype are not
exactly correlated.
 Environment is important.
e.g., human height
 Phenotypic plasticity - the
production of different phenotypes in
response to different environments.
e.g., white oak leaves
• A change in the environment also can
affect the phenotype.
• Pinkness in flamingos is not encoded
into their genotype.
• The food they eat makes their phenotype
white or pink.
Evolutionary Constraint
 All conceivable mutations are not
possible.
The organism must still function.
 All jawed vertebrates have a body plan
with 2 pairs of paired appendages.
 No six legged vertebrates.
 Evolution must work with what it has.
Major reorganization very rare.
Evolutionary Constraint
p. 411
• Why couldn't terrestrial arthropods evolve to
be as large as elephants?
• What is an evolutionary constraint?
The laws of Physics and Inheritance
• Arthropods inherited both an exoskeleton and
jointed legs.
• These traits have opened up many opportunities in
arthropod evolution, but they have also blocked
other possibilities.
• In particular, there are three constraints on the size
of terrestrial arthropods:
– Molting: Molting is more hazardous for larger animals.
– Exoskeleton strength: The exoskeleton may not be
strong enough to support larger animals.
– Respiration: Many arthropods can only get enough
oxygen to support small bodies.
The land-dwelling coconut crab weighs in at 5 kg (over
10lbs). For these giants, molting is a serious commitment:
they may spend a whole month in a deep burrow wriggling
out of the old skin and waiting for the new one to firm up!
Is the physics of molting a
constraint on arthropod size?
You've just seen that molting out of the exoskeleton may limit the
size of terrestrial arthropods. Does the exoskeleton cause other
problems for outsized arthropods? To figure out the answer, we'll
see what happens to the exoskeleton and the muscles that move it
when an arthropod is scaled up.
Exoskeleton strength: Blowing up ants
What would happen to an ant if it were scaled up, keeping all
its body parts in proportion? Each ant below is twice the size of
the previous one.
See what happens when it gets up to go forage for food.
Exoskeleton strength: A solution?
So is there any solution to this problem?
Well, wider tubes are stronger than narrower ones. Perhaps if
we gave our giant ant extra-wide legs with an extra-thick
exoskeleton, it wouldn't suffer so many broken limbs. Does
this ant look like it might be a winner?
Extra large means extra heavy
Test.png
Test.png
The Crustacean/Spider
Model
The
The Insect
Insect Model
Model
Water/air passes over gills/book
gills/book
lungs
and lungs
oxygen
and
diffuses
oxygen
into the
diffusesThe
blood.
intoblood
the blood.
carriesThe
oxygen
throughout
the
body.
blood carries
oxygen
throughout the body.
Tracheae and tracheoles
(essentially ductwork) allow air to
circulate throughout the body —
oxygen diffuses into the tissues
near individual cells.
The Crustacean/Spider Model
Water/air passes over gills/book lungs
and oxygen diffuses into the blood.
The blood carries oxygen throughout
the body.
The Insect Model
Tracheae and trachioles
(essentially ductwork) allow air
to circulate throughout the body
— oxygen diffuses into the
tissues near individual cells.
Respiration: Gotta have oxygen
All animals, including insects, need oxygen. Without it, their
cells die. Insects don't have lungs and their "blood" doesn't
carry oxygen. Insect cells get oxygen via a direct link to the
air outside — a network of tubes, called tracheae let oxygen
reach cells deep within the insect.
All animals, including insects, need oxygen. Without it, their
cells die. Insects don't have lungs and their "blood" doesn't
carry oxygen. Insect cells get oxygen via a direct link to the
air outside — a network of tubes, called tracheae let oxygen
reach cells deep within the insect.
The tubes below represent the tracheae of three dragonflies. In
this model, each tube supplies a gut cell with oxygen — the
larger the dragonfly, the longer the tube. The blue dots represent
oxygen molecules. See how oxygen moves through the tubes.
The gut cell in the biggest dragonfly is not doing too well
because it is not getting enough oxygen. There is a limit to the
length of tracheae (and thus to the size of the dragonfly) that
can provide every cell with sufficient oxygen.
Conclusion
• Evolution is an undirected process, constrained
– by physical laws (such as gravity)
– by genetics (which might, for example, encode the
directions for building breathing organs in a
particular way), and
– by the environment (which might not, for example,
contain a niche for a large, slow-moving, and
fragile ant).
• In the case of the arthropods, the exoskeleton — a
useful adaptation for body support, protection and
water retention as well as their respiratory system,
may have brought evolutionary constraints along with
benefits.