Evolution and the Origin of Life

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Evolution and the Origin of Life
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Origin of Life

• Need to make the monomers of the macromolecules
• Need to make polymers of the monomers
• Need to form cells
• Need to be able to pass information from cell to
  cell

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1. Making the first organic molecules

• Oparin and Haldane believed organic molecules
  could be synthesized from inorganic molecules in
  the early atmosphere
• Early atmosphere had no oxygen which usually
  scavenges electrons so different reactions can
  happen
• Also need a lot of energy to form bonds like
  lightening and radiation from the sun with no
  ozone
• Miller and Urey took H2O, H2, CH4, NH3 although
  the atmosphere was probably more like CO, CO2, N2
  (due to volcanic action) and hit it with
  electricity and were able to make some a.a.,
  sugars, lipids, and nitrogen bases
• Some believe that all organic cmpds were
  originally formed from inorganic molecules
  emitted from hyrdothermal vents in the ocean
  floor
• Some believe they came from space

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2. Must form polymers

• In living things today, need enzymes to form
  polymers
• If dilute monomers in water no reactions
• If drop onto hot sand or rocks can make
  proteins
• Inorganic catalysts like Zn may have helped
  combine polymers
• May have stuck to clay which is charged and
  brought monomers close together

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3. Must form cells

• Formation of Protobionts molecules aggregating
  forming a separate internal environment -
  Chemical reactions can take place within it and
  communicate with outside
• Proteinoids throw some proteins together and
  form microspheres that are selectively permeable,
  can discharge voltage by ion flow like nerves,and
  can divide as add extra protein
• Liposomes mix lipids together to form a lipid
  bilayer, able to engulf smaller liposomes and
  split
• Coacervates mix proteins, nucleic acids, sugars
  and cell assemble if add enzymes get taken
  into coacervate they can then take in molecules
  and chemical react using the enzymes and put
  products out

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4. Must be able to pass instructions to make
molecules or can never improve

• If want to pass info. on must be able to copy it
• Can get RNA to copy itself in a tt/ can act as
  enyzmes
• RNA can fold into many shapes thru b.p.
• Some RNA may become more stable, copy faster
  may be acted on by natural selection

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Evolution Chapter 22

• Taxonomy grouped things to better understand
  them and saw a pattern of relatedness
• Kingdom Phylum Class Order Family Genus
  - Species
• Darwin saw descent with modification all living
  things are descendents of a common ancestor and
  acquired modifications or adaptations that
  allowed them to survive in their environment

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Darwins Finches
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Darwin Evolution Explanation for Unity and
Diversity

• Observation Organisms have more babies than
  survive and resources can only support so much
• Conclusion strongest survive only those that
  can get resources
• Observation There are variations in populations
  (due to mutation and genetic recombination)
• Observation Characteristics best suited to
  survive reproduce more and pass on those char.
• Conclusion Get a gradual change in population
  over time to those best suited

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Darwins Evolution

• 1. Organisms are modified over time (Descent
  with modification)
• 2. Mechanism Natural Selection
• Variation must already be present
• Must be able to survive to reproduce to pass on
  traits to offspring
• Environment acts on inherited variations
  Populations evolve not individuals

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Evidence of Evolution

• Artificial Selection by selecting certain
  natural variations weve created whole new
  organisms
• Ex. Pigeons http//home.iprimus.com.au/spud1/pige
  on_pictures.htm
• Ex. Mustard Plant forms kale, broccoli,
  cauliflower, cabbage, brussel sprouts
• Insecticide treatment of bugs
• Anti-biotic resistant bacteria
• Finches beak size goes up and down due to wet
  vs. dry years
• Peppered Moths

Peppered Moth Video
Darwin's finches
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Examples of Natural Selection
insect mimicry
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Evidence of Evolution

• Taxonomy shows living things are all related
  more similar in structure probably the more
  related
• Biogeography (where species are distributed)
  Organisms living near one another are more like
  each other than organisms living in similar
  environments so came from a common ancestor and
  then adapted to the environment
• Fossil Record fossils show descendancy
  relatedness matches age of fossils
• Dont find different vertebrate classes in the
  same age rock appears to happen chronologically
• Can find transitional fossils linking ancient and
  modern species

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Evidence of Evolution Cont.

• Comparative Anatomy
• Homologous Structures shows relatedness vs.
  individual engineering
• Vestigial Organs left-overs no funtion in
  current times
• Comparative Embryology all vertebrates go
  through the same stages early on
• Biochemistry/Molecular Biology same DNA in all
  organisms looks like modified copies of each
  other (mutations to make different proteins)

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Homologous Structures
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Homologous Structures show evolutionary
relationships and should be used for
classificationAnalogous structures do not show
evolutionary relationship and are not used for
classification
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Comparative Embryology
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Molecular Biology Comparisons
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Hierarchy of Living Things
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Evolution of Populations Chapter 23

• Population groups of same species all living
  together may be geographically isolated but may
  mix some for reproduction but not as often as
  with own
• Gene Pool all the genes available in a
  population
• Genetic Structure frequencies of alleles and
  genotypes
• Hardy-Weinberg the genetic structure of a
  population will stay the same unless acted upon
  by outside factors (normal genetic recombination
  wont change the overall frequencies of alleles
  or genotypes)
• This describes a population that is in
  equilibrium non-evolving and stable

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Hardy-Weinberg Equations

• If there are 2 alleles at a locus pq1
• pfrequency of 1 allele (usu. dominant)
• qfrequency of other allele (recessive)
• Example with genes A and a Aa1
• Chance of getting the AA genotype chance of
  getting A x chance of getting a 2nd A or p2
• Chance of getting the genotype aa chance of
  getting a x chance of getting an a or q2
• Chance of getting Aa (2 ways) (Chance of getting
  A x chance of getting a) x 2 or 2pq

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Hardy Weinberg

• All genotypes must 100
• Therefore
• P2 2pq q2 1
• P2 homozygous dominant
• q2 homozygous recessive
• 2pq heterozygous

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Hardy-Weinberg
A
a
Allelic frequencies A 19/30 0.63 (63) a
11/30 .37 (37) p q 1 .63 .37 1
AA (.63) (.63) .40 (40) aa (.37) (.37) .14
(14) Aa (.37) (.63) 2 .47 (47) aA
.40 .47 .14 1 P2 2pq q2 1
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Uses of Hardy-Weinberg

• Calculate the genotypic frequencies if know
  alleles or calculate allelic freq. if know
  genotypes
• Example 1

a 40 alleles 160 200/1000 20 or .2 A 640
alleles 160 800/1000 80 or .8 A a 1
20/500 plants are white (aa) 320/500 are red
(AA) 160/500 are pink (Aa)

• Example 2

2pq Aa Or p2 2pq q2 1 .41 x
.13 1 X .46 (46 of population is carries the
gene
13 of population is homozygous recessive q2
.13 q .36 p q 1 P .64
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Uses of Hardy-Weinberg

• Use equation to calculate what frequencies
  expected in next generation to see if population
  is changing
• If genetic structure is changing then the
  population is evolving
• Microevolution change in genetic structure from
  one generation to the next.
• May have microevolution of some loci and not
  others

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Hardy/Weinberg PracticeTesting for H/W
Equilibrium

• If a population is in H/W equilibrium, the
  genotypes will match H/W predictions given the
  allelic frequencies
• 4 of a population has sickle cell anemia
  (recessive trait)
• Calculate the frequencies for all 3 genotypes
• In this particular process 60 of the people are
  heterozygous and 36 do not have an allele for
  sickle cell.
• Draw a conclusion based on the expected and
  actual data make a hypothesis why they are
  different.

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The interlocking finger conundrum

• In a small isolated village of 2000 people, 1400
  peoples left thumb ends up on top when they
  interlock their fingers.
• Calculate p and q for this population.
• A few centuries later, this population has grown
  to 5000 people, and there are now 2000 left thumb
  on top people. Calculate p and q.
• It is doubtful that there is any selection going
  on here. Propose other mechanisms for the
  allelic change.

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Microevolution Deviation in the Hardy-Weinberg
Equation (i.e. changes in an allelic frequency
over generations)

• There are 4 things that can change the genetic
  structure of a population over time beside
  mutation
• What are these mechanisms? Read about each one
  on pages 475-479. Each group member will read
  about one (non-random mating, genetic drift
  (founder and bottleneck), gene flow. You can
  also read about natural selection if you think it
  is necessary. Take turns explaining each one.

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Microevolution Continued

• You will illustrate each of these mechanisms of
  allelic change based on a story about a community
  of angry birds.
• Mutations are the underlying factor of the other
  4 mechanisms of allelic change so we wont
  illustrate mutation by itself.
• Now lets go to our story

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Its Now 2075
What is the Red Angry Bird Population Like Now?

• Pick one gene
• Eyebrow gene allele 1 V-shaped
• allele 2 sunglass like
• Head Feather allele 1 rounded
• gene allele 2 pointed
• Eye gene allele 1 regular
• allele 2 glowing

For the gene you chose and the mechanism you are
assigned, make up a plausible and creative story
to explain the mechanism incorporating
environmental factors and correct terminology
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What Causes Deviation From Hardy Weinberg?

• Genetic drift changes due to chance only
  improvement would be luck
• Larger populations more closely reflects
  frequency of past generations smaller
  populations will tend to change by chance
• Factors that increase genetic drift
• Bottleneck disasters kill off a bunch
  remaining small population isnt representative
  of original population drift more
• Founder a small group colonizes an island
  small group will tend to not be representative of
  whole group

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Deviations from Hardy-Weinberg

• Gene Flow genetic exchange interaction of one
  pop. with another
• May be due to migration, wind, etc.
• Ex. Other pop. has more aa due to local
  environment so increases freq. in other
  population
• Mutations change in one allele to another must
  be in gamete
• Infrequent and usually causes small variation so
  by itself doesnt change pop. much
• Provides variation for selection
• (Dont forget genetic recombination)

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Deviations from Hardy-Weinberg

• Non-random Mating in-breeding,
  self-fertilization, only mating in close
  proximity, mating based on selective
  characteristics
• All usually increase homozygosity
• Natural Selection Hardy-Weinberg assumes
  that all genotypes have the same ability to
  survive and reproduce which isnt true this is
  probably the major factor controlling evolution

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Evolution Deviation from Hardy-Weinberg

• Anyone of the previous things can cause evolution
  but natural selection acts on all changes to
  determine what allele has the highest
  concentration over time so with natural selection
  a disproportionate of alleles are passed to the
  next generation
• Natural Selection is the only adaptive mechanism

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Evolution Needs variation

• Variation must be present though for anything to
  change therefore mutation and recombination must
  be at the root
• Variations must be heritable or cant effect
  evolution
• However, many mutations wont make a difference
  due to
• Reduncancy of the genetic code
• Mutation in non-coding regions
• Mutations in genes not expressed
• Mutations not in germ cells
• Changes that arent adaptive

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Measuring Genetic VariationPolymorphisms

• How many loci arent fixed
• Average of loci that are heterozygous
• Nucleotide diversity - of nucleotides different
  compare DNA between 2 individuals and pool data
  from many comparisions
• Our genetic diversity among humans is 14 by gene
  or loci, but our nucleotide diversity is 0.1 so
  with 6 x 109 b.p about 6 x 106 are different or
  out of every 1000 b.p. 999 are the same

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Once have variation Evolution need selective
pressure

• Selective Pressure between populations is due to
  geographic variation (different local conditions)
  acts upon previous mutations to change genetic
  structure and may create subpopulations or clines
• Selective Pressure within populations is due to
  competition for food, homes, mates,
  environmental conditions (weather),

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Types of Natural Selection

• Stabilizing select against the extremes (human
  birth weight)
• Directional during environmental changes or
  migration, shifts to a new phenotype (bird beaks,
  scale sucking fish)
• Diversifying selects for both extremes (finches
  in Africa selects against medium beak that
  isnt good at cracking either food sourced)
• Separate Selection based on sex leads to sexual
  dimorphism (selected by
• pressure to mate)

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Natural Selection Should Lead Away from Diversity
soWhy do populations remain diverse?

• Diploidy hides variation from selection
  heterozygous conditions keeps alleles in
  population since recessive alleles cant be acted
  on by selection when coupled with a dominant one
  (protects alleles not suited to environment)
• Balanced Polymorphisms
• 2 variations may work the best
• Heterozygous advantage Aa works best
• Alternating selective pressure, diversitying
  selective pressures
• Neutral Effects variations make no difference
  (not adaptive) but may become adaptive later
• Not alter reproductive fitness (Huntingdons)

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Why Populations Remain Diverse

• Continued Mutation the same mutation may keep
  arising like in neurofibromatosis
• 1/4000 spontaneous gamete mutations
• Gene Flow gene may not be deleterious in a
  nearby population (ex. Sickle cell allele)
• Natural Selection may not have had time to remove
  the allele yet may have not been deleterious
  previously and is now being selected against but
  not yet gone (ex. Cystic fibrosis in Caucasians
  allele gives resistance to cholera)

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Speciation

• New species appear in rock where did they come
  from? How did new species form?
• Species can interbreed and produce fertile
  offspring under natural conditions physically
  and biochemically distinct not just mixtures
• Anagenesis one species transforms into another
• Cladogenesis an ancestor produces one or more
  different variations and all exist simaltaneously
  (increases the of species)

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Why species remain distinct

• Pre-zygotic Barriers
• Habitat Isolation live in different areas
• Behavioral Isolation mating rituals, firefly
  lighting patterns
• Temporal Isolation different mating times
  (seasonal), different times of flowering,
  nocturnal vs. day
• Mechanical Isolation physically impossible to
  mate
• Gametic Isolation gametes cant match up

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Why Species remain distinct

• Post-zygotic Barriers
• Poor Hybrid viability embryos die
• Poor Hybrid fertility offspring cant reproduce
• Hybrid Breakdown make a weak or sterile second
  generation

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Origin of New Species members must become
separated so acted on differently by natural
selection

• Allopatric Speciation a population becomes
  separated by a physical barrier have different
  selective pressures after separation
• Examples
• migration to different islands
• New mountain separates them
• Lake dries up to multiple little ponds

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Origin of New Species Cont.

• Sympatric Speciation a population becomes
  reproductively isolated but still lives with the
  parent population
• Examples
• Plant that becomes polyploid can only reproduce
  with other polyploid plants and not others of its
  kind (25-50 of plants oats, cotton, potatoes,
  tobacco)
• Animals genetic change causes a difference that
  keeps them from mating may eat a different food
  source and dont mate with others eating a
  different food source. May become adapted to
  live on a certain plant and never meet the group
  living on a different plant
• Sex Selection may play a role (females only mate
  with males with a certain trait)

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Why evolution takes places once a population
becomes separated

• Organisms on the edge are usually different
  anyway
• Founder effect (small group leaving may not be
  representative of whole)
• Genetic Drift
• Neutral mutations may become fixed without
  selective pressures due to small population size
• Different selective pressures
• Therefore Microevolution over time slowly
  changes each population

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• This is called adaptive divergence adapt to
  environment which causes a 2ndary reproductive
  isolation
• Sometimes there are adaptive peaks may have
  several forms that are optimized for success
  (more than 1 selective pressure) and chance may
  cause to a change in form or environment may
  slowly change causing a shift from 1 peak to
  another

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What happens if separated species come back
together?

• May interbreed and become a mix
• May stay separate due to reproductive barriers
• Hybrid Zone only interbreed where overlap and
  other parts of population remain separate
• If there arent true reproductive barriers
  still a separate species?

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Macroevolution

• substantial change in organisms
• Origin of taxonmic groups higher than species
• Origin of new phyla, classes, orders, families
• Is it due to the cumulative product of
  microevolution or some big event or????
• The appearance of flowering plants seems to be
  all at once?????
• The appearance of mammals seems to be all at
  once?????

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Punctuated Equilibrium

• Big changes (episodes of speciation) followed by
  slow gradual change (if optimized for environment
  shouldnt be a lot of change due to selection
  unless large change in selection pressures)
• Due to quick geographic separation and genetic
  drift
• Due to sudden genome changes
• Changes may not be shown in fossils

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Fossils

• Organic parts of dead organisms decay rest of
  inorganic material like shells etc. remain in
  sedimentary rock
• Minerals may replace organic part of dead
  organisms and harden it which preserves it
  (petrification)
• May leave a mold (imprint) in rock that is later
  hardened by minerals (makes a cast) May be
  footprints, burrows, things that leave hints of
  behavior
• Whole organism may be preserved in the absence of
  decomposers like in amber, ice, acid bogs, dry
  areas
• Dead organism pressed between rocks may
  preserve even organic parts like cells
  sometimes pollen is preserved because it is in a
  hard case

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Fossils continued

• Most fossils would be organisms that lasted a
  long time, were abundant, had shells or hard
  skeletons
• Any fossils found are by luck
• Had to wash with sediments
• Rock had to last untouched
• Had to be exposed
• Had to be found

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Dating Fossils

• Sedimentation isnt uniform rocks are found in
  layers or strata the further down the stack,
  the older it is (only relative age)
• Correlate age of strata from 1 place to another
  by similar strata with same fossils
• Based on times of great change between strata,
  mass extinction followed by an explosion in
  adaptive radiation divides Earths history into 4
  eras Precambrian, Paleozoic, Mesozoic, Cenozoic

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Radiometric Dating

• Use ½ life of radioactive elements
• Time it takes for 50 to decay
• Know ratio of C-14/C-12 in living things
• Measure how much relative C-14/C12 now and can
  tell how many ½ lives
• Example Fossil has ¼ C-14/C-12 as living
  organism 2 ½ lives to get age take ½ life
  of C-14 x 2.

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Dating Questions

• How do we know that ½ life is a steady decay
• How do we know it isnt altered by climate
• How do we know fossil had same ratio as living
  organisms today
• How accurate is the measure of C-14/C-12
• Error is 10 - how do you measure error?

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Mechanisms of Macroevolution

• Pre-adaptation structure is adapted for 1 thing
  and later used for another function (gradual
  change in existing structure leads to a new
  function)
• Example lattice-like bones of birds some
  dinosaurs had it but must have had another
  function
• Changes in developmental genes
• Heterchrony changes in developmental timing or
  rate
• Homeosis alteration in placement of body parts

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Developmental Gene Changes

• Examples
• Allometric growth differences in relative rate
  of growth of a certain part during development
  like skull bones and brains
• Padeomorphosis change in developmental timing
  adult keeps characteristics of juvenile form of
  ancestor

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Changes in genes that control rate of growth or
developmental timing can make big changes
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Mechanisms of Macroevol. Cont.

• Species Selection things evolve into other
  species or may branch into other species and only
  strongest species survives
• Mass Extinction due to huge geographical
  changes (climate, destruction of habitats)
  leaves it open for species to fill new places
  adaptive radiation

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• Examples Continental Drift
• End of Paleozoic Pangaea formed
• Permian extinction species now in competition
  with things never saw before
• Less shore-line, extreme volcanism with great
  temperature effects
• Mass extinction (90 species gone) chance for
  new species
• Early Mesozoic Pangaea breaks up geographical
  isolation
• Formation of mountains, new islands, earthquakes

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Mass Extinction causing Macroevolution Cont.

• Cretaceous Extinction possible asteroid hit
  large layer of rock made of sediments found in
  asteroids but not on earth (large craters
  present)
• loss of more than 50 of marine species
• Cooler tempatures, shallow seas receded
• With any of these times of mass extinction
  surviving species are a stock for new radiations,
  fossils do show periods of mass extinction and
  adaptive radiations, organisms filling the void
  left by others

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Mechanisms of Macroevolution Cont.

• Accumulation of Microevolution not preserved in
  fossil record or intermediates not found due to
  small numbers

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CladogramsDiagrams that show probable
relationships between the taxa, sequence of
origin, common ancestors, shared characteristics
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Systematics study of biodiversity in an
evolutionary context

• Want to decide an organisms taxa based on
  evolutionary relationships
• How do scientists decide?
• Comparative Anatomy
• Analogous structures similar due to like
  environments, built from different structures
  (ex. Wings or birds and insects)
• Homologous structures similar due to common
  structure and therefore common ancestry (ex. Wing
  of bat, whale fin, arm of human, paw of dog)
• Should only use homologous structures for
  classificaiton
• Problem with comparative anatomy like
  structures not necessarily from common ancestor
  may be due to convergent evolution shaped by
  same environmental factors

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Systematics classifying cont.

• Proteins closer the aa sequence probably from
  a closer common ancestor
• DNA closer nucleotides sequences more related
  (dolphins are closer to bats than sharks)
• Can extract DNA from fossils
• DNA-DNA Hybridization see overall similarity of
  genomes by checking amountof H-bonding between 2
  ss DNAs from 2 different organisms
• Restriction Mapping
• DNA sequencing compare rRNAs to look for
  branching since seems to have changed the slowest
• Molecular clocks if rate of DNA change is
  constant and can calculate when diverged using
  fossils dating can calculate the rate of DNA
  change/time

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Summary of Macroevolution

• May be due to rapid changes
• Mass separations
• Rapidly changing environments
• Chromosomal or developing genes mutating
• Mutations acted upon by huge genetic drift and
  selection
• Mass extinctions causing adaptive radiations

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Remaining Questions about Macroevolution

• Could it really be compounded microevolution?
• What is gradual vs. quick?
• Is the fossil record complete?
• Do different mechanisms work at different levels?