Transcript Evolution and the Origin of Life

Evolution and the Origin of
Life
Origin of Life
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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
1. Making the first organic
molecules
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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
2. Must form polymers
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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
3. Must form cells
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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
4. Must be able to pass instructions to
make molecules or can never improve
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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
Evolution – Chapter 22
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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
Darwin’s Finches
Darwin – Evolution – Explanation for
Unity and Diversity
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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
Darwin’s 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
Evidence of Evolution
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Artificial Selection – by selecting certain natural
variations – we’ve created whole new organisms
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Ex. Pigeons
http://home.iprimus.com.au/spud1/pigeon_pictures.htm
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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
Examples of Natural Selection
insect mimicry
Evidence of Evolution
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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
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Don’t find different vertebrate classes in the same age rock –
appears to happen chronologically
Can find transitional fossils linking ancient and modern
species
Evidence of Evolution Cont.
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Comparative Anatomy
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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)
Homologous Structures
Homologous Structures show evolutionary relationships and
should be used for classification
Analogous structures do not show evolutionary relationship
and are not used for classification
Comparative Embryology
Molecular Biology Comparisons
Hierarchy of Living Things
Evolution of Populations
Chapter 23
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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 won’t change the overall
frequencies of alleles or genotypes)
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This describes a population that is in equilibrium –
non-evolving and stable
Hardy-Weinberg Equations
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If there are 2 alleles at a locus: p+q=1
p=frequency of 1 allele (usu. dominant)
q=frequency of other allele (recessive)
Example with genes A and a: A+a=1
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
Hardy Weinberg
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All genotypes must = 100%
Therefore:
P2 + 2pq + q2 = 1
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P2 = homozygous dominant
q2 = homozygous recessive
2pq = heterozygous
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
Uses of Hardy-Weinberg
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Calculate the genotypic frequencies if know
alleles or calculate allelic freq. if know genotypes
Example #1:
20/500 plants are white (aa)
a: 40 alleles + 160 =
200/1000 = 20% or .2
320/500 are red (AA)
A: 640 alleles + 160 =
800/1000 = 80% or .8
160/500 are pink (Aa)
 Example # 2:
13% of population is homozygous
recessive
q2 = .13
p+q=1
P = .64
q = .36
A+a=1
2pq = Aa
Or
p2 + 2pq + q2 = 1
.41 + x + .13 = 1
X = .46 (46% of population
is carries the gene
Uses of Hardy-Weinberg
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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.
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May have microevolution of some loci and not
others
Hardy/Weinberg Practice
Testing for H/W Equilibrium
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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.
The interlocking finger
conundrum
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In a small isolated village of 2000 people, 1400
people’s 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.
Microevolution
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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.
Microevolution Continued
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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 won’t illustrate mutation by itself.
Now lets go to our story
It’s 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
gene
allele 1: rounded
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
What Causes Deviation From Hardy –Weinberg?
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Genetic drift – changes due to chance – only
improvement would be luck
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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 isn’t
representative of original population – drift
more
 Founder – a small group colonizes an island –
small group will tend to not be representative
of whole group
Deviations from Hardy-Weinberg
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Gene Flow – genetic exchange –
interaction of one pop. with another
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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
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Infrequent and usually causes small variation
so by itself – doesn’t change pop. much
Provides variation for selection
(Don’t forget genetic recombination)
Deviations from Hardy-Weinberg
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Non-random Mating – in-breeding, selffertilization, 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 isn’t
true – this is probably the major factor
controlling evolution
Evolution – Deviation from HardyWeinberg
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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
Evolution: Needs variation
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Variation must be present though for anything
to change therefore mutation and recombination
must be at the root
Variations must be heritable or can’t 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 aren’t adaptive
Measuring Genetic Variation
Polymorphisms
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How many loci aren’t 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
Once have variation – Evolution
need selective pressure
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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),
Types of Natural Selection
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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 isn’t
good at cracking either food sourced)
Separate Selection based on sex – leads to
sexual dimorphism (selected by
pressure to mate)
Natural Selection Should Lead Away
from Diversity so…
Why do populations remain diverse?
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Diploidy – hides variation from selection –
heterozygous conditions keeps alleles in
population since recessive alleles can’t 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 (Huntingdon’s)
Why Populations Remain Diverse
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Continued Mutation – the same mutation may
keep arising like in neurofibromatosis
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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)
Speciation
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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)
Why species remain distinct
Pre-zygotic Barriers
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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 can’t match up
Why Species remain distinct
Post-zygotic Barriers
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Poor Hybrid viability – embryos die
Poor Hybrid fertility – offspring can’t
reproduce
Hybrid Breakdown – make a weak or
sterile second generation
Origin of New Species – members
must become separated so acted on
differently by natural selection
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Allopatric Speciation – a population
becomes separated by a physical barrier –
have different selective pressures after
separation
Examples
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migration to different islands
New mountain separates them
Lake dries up to multiple little ponds
Origin of New Species Cont.
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Sympatric Speciation – a population becomes
reproductively isolated but still lives with the
parent population
Examples
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Plant that becomes polyploid can only reproduce with
other polyploid plants and not others of its kind (2550% of plants – oats, cotton, potatoes, tobacco)
Animals – genetic change causes a difference that
keeps them from mating – may eat a different food
source and don’t 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)
Why evolution takes places once a
population becomes separated
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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
What happens if separated species
come back together?
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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 aren’t true reproductive barriers –
still a separate species?
Macroevolution
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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?????
Punctuated Equilibrium
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Big changes (episodes of speciation) followed by
slow gradual change (if optimized for
environment – shouldn’t 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
Fossils
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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
Fossils continued
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Most fossils would be organisms that
lasted a long time, were abundant, had
shells or hard skeletons
Any fossils found are by luck
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Had to wash with sediments
Rock had to last untouched
Had to be exposed
Had to be found
Dating Fossils
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Sedimentation isn’t 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 Earth’s history into 4
eras: Precambrian, Paleozoic, Mesozoic,
Cenozoic
Radiometric Dating
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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.
Dating Questions
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How do we know that ½ life is a steady
decay
How do we know it isn’t 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?
Mechanisms of Macroevolution
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Pre-adaptation – structure is adapted for 1
thing and later used for another function
(gradual change in existing structure leads
to a new function)
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Example – lattice-like bones of birds – some
dinosaurs had it but must have had another
function
Changes in developmental genes
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Heterchrony – changes in developmental
timing or rate
Homeosis – alteration in placement of body
parts
Developmental Gene Changes
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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
Changes in genes that control rate
of growth or developmental timing
can make big changes
Mechanisms of Macroevol. Cont.
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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”
Examples: Continental Drift
 End of Paleozoic – Pangaea formed
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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
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Formation of mountains, new islands,
earthquakes
Mass Extinction causing
Macroevolution Cont.
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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
Mechanisms of Macroevolution
Cont.
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Accumulation of Microevolution not
preserved in fossil record or intermediates
not found due to small numbers
Cladograms
Diagrams that show probable relationships between the taxa, sequence
of origin, common ancestors, shared characteristics
Systematics – study of biodiversity in
an evolutionary context
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Want to decide an organisms taxa based on
evolutionary relationships
How do scientists decide?
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Comparative Anatomy
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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
Systematics – classifying cont.
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Proteins – closer the aa sequence – probably
from a closer common ancestor
DNA – closer nucleotides sequences – more
related (dolphins are closer to bats than sharks)
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Can extract DNA from fossils
DNA-DNA Hybridization – see overall similarity of
genomes by checking amountof H-bonding between 2
ss DNA’s from 2 different organisms
Restriction Mapping
DNA sequencing – compare rRNA’s 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
Summary of Macroevolution
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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
Remaining Questions about
Macroevolution
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Could it really be compounded
microevolution?
What is gradual vs. quick?
Is the fossil record complete?
Do different mechanisms work at different
levels?