Transcript Evolutionary Biology - Doral Academy Preparatory

LIFE’S ORIGIN AND
EARLY EVOLUTION
Early Earth & Geologic Time
 3 eons
 Phanerozoic (present-542 mya)
 Proterozoic ( 542 mya- 2500 mya)
 Archaean (2500 mya-4600mya)
Phanerozoic Era
 Divided into eras, periods and epocs
 Cenozoic era (present-65.5 mya) includes 4o and 3o
periods.
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Adaptive radiation of mammals, insects and birds.
Emergence of woodland and grassland.
Evolution of humans.
Possible extinction underway
 Mesozoic era (65.5 mya- 251 mya)
 Cretaceous, Jurassic, and Triassic periods (3 major
mass extinctions)
 Appearance and extinction of dinosaurs.
 Appearance of turtles, small mammals,
gymnosperms, and ferns.
 Pangea broke up (continental drift)
 Climate warming.
 Paleonzolic Era (251 mya-542 mya)
 3 major extinctions as well..
 Emergence of marine animals.
 Radiation of marine invertebrate
 Land plants
 Diversification of insects, amphibians, and
reptiles.
 Oceans formed at the end.
Proterozoic Eon
 Atmospheric accumulation of O2.
 Origin of eukaryotic cells
Archaean Eon
 Earth’s crust formed
 Atmosphere
 First seas
 First prokaryotes
Organic Compounds & First Cells
 13-15 bya: universe formed
 4 bya: Earth formed
 First atm Earth crust and first seas molecular
evolution  protocell  prokaryote  eukaryote
Clay hypothesis
 A.a. stuck to clay, forming proteins when
energized by the sun.
 A.a. could have bonded to form proteins near
the deep-sea hydrothermal vents.
 Both support the idea that protein enzymes
need to be in place before any other chem.
Rxn like replication or metabolism can take
place
RNA first hypothesis
 RNA in the form of ribozymes, can act like
enzymes that are needed for protein
synthesis and would therefore precede
protein and DNA systems.
Formation of first cells
 A.a form long chains of proteins
 Fatty acid and alcohols will form sacs around
clay.
 Proteins + lipids + water = membrane-like
structure similar to the phospholipid bilayer
membrane of cells.
 Lead to protocells (could replicate) first
prokaryote.
Organizing Information About Species
CHAPTER 19
19.4-Comparing DNA and Proteins
 Kinds and numbers of biochemical similarities
among species reflect evolutionary
relationships
 DNA and amino acid sequence differences
are greatest among lineages that diverged
long ago, and less among recently diverged
lineages
Remember that…
1. Mutations are random and can occur anywhere
on the DNA
2. Most mutations are neutral
3. Neutral mutations help to identify when
lineages diverge
4. Correlating changes in DNA with morphological
changes in fossil record can help correlate
common lineages
5. Essential genes (cytochrome B) are more
guarded = harder to mutate
Cytochrome C= federal reserve
Molecular Comparison:
 A.a. sequence comparison can be used to
determine species relationships.
 Single substitution may have large or small
effects based on the amino acid that is
replaced and what it is replaced with.
 Mitochondrial DNA= used to determine
familiar relationships because it is passed
down without the effects of crossing over
(mom’s side)
Making Data into Trees
 Parsimony analysis; determines the most
logical connections between species.
 Rule of cladistics: simplicity guides
relationships, the closer a relationship
amongst species, the least amount of
difference
 Evolutionary trees with the fewest
differences are more likely to be correct.
 Platypus ancestry
www.nature.com/news/2008/080507/full/453
138a.html
CHAPTER 18-PROCESSES OF
EVOLUTION
Individuals don’t evolvepopulations do
 Genetic variation exists amongst population,
but they also hold certain morphological,
physiological and behavioral traits on
common
Gene Pool
 All of the genes in the entire population constitute
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the gene pool
Each gene exists in tow or more slightly different
molecular forms called alleles, which offspring
inherit and express as phenotypes (Aa)
Dimorphism: two variation of a trait in a population
Polymorphism: 3 or more variations of a trait.
Offsprings inherit genotypes NOT phenotypes.
Environmental phenotypes are caused by adaptation
and therefore are NOT inherited.
Mutations Revisited
 HERITABLE changed in DNA that can alter
gene expression
 Random= neutral, beneficial, harmful or
lethal depending on other interactions.
 THE ONLY SOURCE OF NEW ALLELES- the
genetic foundation for biological diversity.
HARMFUL, BENEFICIAL, NEUTRAL OR LETHAL?
Harmful, beneficial, neutral,
lethal?
Stability and Change in Allele
Frequencies
 Measure of abundance of each kind of allele
in the entire population
 Change in allele frequency= evolution (shift in
the genetic equilibrium)
 Hardy-Weinberg rule (coming up!!)
Stable populations
1. no mutation are occurring
2. The population is very, very large
3. Population is isolated from other populations
of the same species
4. All members survive, mate, and reproduce (
no selection)
5. Mating is random
NATURAL POPULATIONS ARE
NEVER IN GENETIC
EQUILIBRIUM
Microevolution
 Change in frequency brought on by
 Mutation
 Genetic drift
 Gene flow
 Natural selection
 Small scale changes in allele’s frequency prevent
genetic equilibrium
A population in equilibrium
Natural Selection
 Most influential microevolutionary process
 An allele that ensure better survival will
influence frequency.
 3 major categories of selection
 Directional
 Stabilizing
 Disruptive
Directional selection
 Shifts allele
frequencies in a
consistent direction.
 Traits at one end of the
freq. becomes more and
more prominent.
 In response to
environmental
pressures.
 As a new mutation
appears and is adaptive.
E.g.: Pocket Mice
 Habitat: Arizona
desert.
 Light colored fur blend
in with the granite.
 Smaller pop’n w/
darker coat blends in
with dark basalt.
 Selective Pressure?
Resistance in Antibiotics
 A typical two-week course of antibiotics can exert
selection pressure on over a thousand generations of
bacteria
 Antibiotic resistant strains are now found in hospitals and
schools
Stabilizing Selection
 Favors the most common phenotype in the
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population
Weaver birds in the African savanna.
Body weight is a tradeoff between the risks of
starvation and predation.
Leaner birds vs. fatter birds?
Pros and cons….which trade wins?
Disruptive Selection
 Favors forms at the extremes of the
phenotypic range.
 African finches have either large or small
sized beaks. No in between.
 Smaller billed birds fed on soft seeds.
 Larger billed birds fed on harder seeds.
 Show animations now
 Stabilizing selection
 Disruptive selection
 Adaptation to what
 Change in moth population
 African finches
Maintaining Variation in
Population
 Sexual Selection
 Most males of a specie are larger, more colorful,
more aggressive or have a special courtship
behavior. Sometimes these traits are
maladaptive.
 Based on any trait that gives a competitive edge in
mating.
Balanced polymorphism
 Humans that are homozygous for sickle-cell
anemia (Hbs/Hbs) develop the disease and
die at an early age.
 Individuals with alleles for both normal
hemoglobin (Hba) and sickle-cell hemoglobin
(Hbs) have the greatest chances of surviving
malaria.
 Sickle-cell allele persists in the pop’n despite
its relative disadvantage.
Genetic drift
 Random fluctuation in allele frequencies over
time, DUE TO CHANCE ALONE.
 May lead to a homozygous condition
 Occurs faster in smaller populations.
 One kind of allele remains at a specified locus in a
population. (fixation)
Bottleneck
vs.
Founder Effect
 Stressful situation reduces
 Few ind. (carrying genes
pop’n size, leaving few ind.
to reestablish the pop’n.
 This bottleneck decreases
the genetic diversity and
can be a cause of genetic
drift
that may or may not be
typical of the whole
population) leave the
original population to
establish a new one.
 Diversity is limited,
random effect of drift.
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An example of a bottleneck:
Northern elephant seals have reduced genetic variation probably because of a
population bottleneck humans inflicted on them in the 1890s. Hunting reduced their
population size to as few as 20 individuals at the end of the 19th century. Their
population has since rebounded to over 30,000—but their genes still carry the marks
of this bottleneck: they have much less genetic variation than a population of
southern elephant seals that was not so intensely hunted.
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Founder effects
A founder effect occurs when a new colony is started by a few members of the
original population. This small population size means that the colony may have:
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reduced genetic variation from the original population.
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a non-random sample of the genes in the original population.
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For example, the Afrikaner population of Dutch settlers in South Africa is descended
mainly from a few colonists. Today, the Afrikaner population has an unusually high
frequency of the gene that causes Huntington’s disease, because those original Dutch
colonists just happened to carry that gene with unusually high frequency. This effect
is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of
genes are affected by founder events.
Inbreeding
Ellis-van Creveld Syndrome
 Breeding or mating between
close relatives who share a
large number of alleles
 Example: Old Order Amish in
Lancaster County,
Pennsylvania (Ellis-van
Creveld syndrome
 It involves numerous anomalies
including post-axial polydactyly,
congenital heart defects (most
commonly an atrial septal defect
producing a common atrium,
occurring in 60% of affected
individuals), pre-natal tooth
eruption, fingernail dysplasia,
short-limbed dwarfism, short
ribs, cleft palate, and
malformation of the wrist bones
(fusion of the hamate and
capitate bones).
Gene Flow
 Genes move with ind. Whey they move out of
or into a population.
 Microevolutionary process that reduces the
effect of mutations, selection, and drift in a
population.
 Gene flow could lead to genetically modified
genes entering a wild population.
Reproductive Isolation
 Speciation: evolutionary process by which
new species are formed.
 Reproductive isolation is necessary for
speciation to occur, hence necessary for
evolution.
 The end of gene exchange between populations
 The beginning of speciation.
 The wood frog and leopard
frog have different peaks
of mating activity, this
prevents any
interbreeding.
Behavioral Isolation:
Behavioral Isolation is when two populations, because of facing
differing sexual selection pressures, will acquire different mating
rituals and behaviors. Some organisms within a population will not
breed with another organism if it doesn’t have the same mating
rituals. In the birds in the follow picture, the mating ritual in the left
differs from the mating ritual on the right, and if a bird (even
though they look the same) tries to present the ritual between the
two variations, the female will not breed with them.
 Show animations
 Albatross courtship
 Reproductive isolating mechanisms
Allopatric Speciation
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Allopatric Evolution:
This is the most basic form of evolution. When a population of organisms is
separated by physical barriers, they will face different selection pressures
that select for different alleles. Over time, the split population will diverge
enough that if the two populations ever crossed paths again, they would be
unable to interbreed (or they may breed, but they would produce sterile
hybrids, like the liger or mule).
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E.g: llamas and camels and vicunas (allopatric)
Peripatric evolution is a form of allopatric evolution, but when one
population is significantly smaller than the other.
Peripatric Speciation
Sympatric Speciation
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This is when organisms evolve in either overlapping or identical
environments. This is very similar to parapatric speciation, which is generally
referred to when behavioral sexual isolation occurs. One way in which
sympatric evolution occurs is in a rain forest, there are several different
environments – for example, the canopy and the ground. A single
population of insects may separate into two, with one facing different
selection pressures in the canopy while the others face a very different
pressure on the ground. There is also the famous (in biology circles) Chiclid
fish in Africa.
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In three lakes of Africa’s Rift Valley, a
member of a family of fish named
cichlids has evolved a range of
ecologies and sizes unmatched
anywhere else. Those lakes are
known to have formed no later than
1.5-2 million years ago, and the
hundreds of species of fish in those
lakes occupy ecological niches, and
exhibit biological forms, unheard of
elsewhere. (One species specializes
in eating the eyes of other fish.) The
range is greater than what you
might find at a coral reef, and all
from a small number of evolutionary
starting points.
Macroevolution
 Occurs at a much larger scale
 Includes patterns of change such as one species
giving rise to multiple species, the origin of major
groups, and major extinction events
Other patterns of speciation
 Coevolution: caused by ecological
interactions like predator-prey
 Stasis: long term lineage with relatively little
evolutionary change (a lot of reptile lineages)
 Exaptation: appearance of a trait that was
originally used for something else (feathers in
birds and dinosaurs)
 Extinction: fossil records indicate more that
20 mass extinctins. Each one followed by a
period of adaptive radiation.