Chapter 16Chapter 16Evolution of PopulationsEvolution of Populations

16.1 Genes and Variation16.1 Genes and VariationA. Populations and Gene PoolsA. Populations and Gene Poolsa. populationa. population: individuals of the same species in a : individuals of the same species in a

given given area.area.

b. gene poolb. gene pool is the combined genetic material of all is the combined genetic material of all thethe

alleles in the populationalleles in the population c.c. allele frequencyallele frequency = % of an allele in the pool = % of an allele in the pool

* 20 bugs =the gene pool has 40 alleles * 20 bugs =the gene pool has 40 alleles (some B, b)(some B, b)

30 B alleles = .7530 B alleles = .7510 b alleles = .2510 b alleles = .25

Genes are responsible for the phenotypes Genes are responsible for the phenotypes in organismsin organisms

if the frequency of allele changes, then the if the frequency of allele changes, then the population will start to look different as population will start to look different as nature selects for these alleles. – breeding nature selects for these alleles. – breeding bunnies for examplebunnies for example

In genetic terms = evolution is any change In genetic terms = evolution is any change in the relative frequency of alleles in a in the relative frequency of alleles in a population. population.

B. Sources of Genetic VariationB. Sources of Genetic Variation Evolution is fueled by variations in Evolution is fueled by variations in

individualsindividuals

that result from sexual reproduction:that result from sexual reproduction:

a. Mutationsa. Mutations

crossing over in meiosis

random homologous pairing in meiosis

b.b.Gene ShufflingGene Shuffling During meiosis independent assortment During meiosis independent assortment

and crossing over increase the number of and crossing over increase the number of genotypes that can occur.genotypes that can occur.

C. Expression of VariationC. Expression of Variation

a. Some traits are a. Some traits are single-allele traitssingle-allele traits

example: widow’s peak. example: widow’s peak.

2 alleles and 2 phenotypes2 alleles and 2 phenotypes

b. Most traits are b. Most traits are polygenic trait.polygenic trait.

Controlled by 2 or more genes Controlled by 2 or more genes

There is a lot of variation in the phenotype There is a lot of variation in the phenotype

Ex: height, hair colorEx: height, hair color

A lot of variation in Polygenic traits

Two forms of the trait in single allele traits

16.2 Evolution as Genetic Change16.2 Evolution as Genetic Change

A. What causes allele frequencies in a geneA. What causes allele frequencies in a gene

pool to change?pool to change?

1. Natural Selection on Single Allele Traits1. Natural Selection on Single Allele Traits

If an organism survives and produces If an organism survives and produces manymany

offspring, its alleles stay in the gene pool and offspring, its alleles stay in the gene pool and

may may increaseincrease in frequency. The adaptations in frequency. The adaptations

that helped it to survive will be magnified.that helped it to survive will be magnified.

Example: Breeding Bunnies fur or no furExample: Breeding Bunnies fur or no fur

2. Natural Selection on Polygenic2. Natural Selection on Polygenic TraitsTraits

With many phenotypes, distribution of traits can With many phenotypes, distribution of traits can

be affected in may waysbe affected in may ways..a. Directional Selectiona. Directional Selection

When individuals at one end of the of the curve When individuals at one end of the of the curve have have

higher fitness than the middle or the other end.higher fitness than the middle or the other end.

Food becomes scarce.Key

Low mortality, high fitness

High mortality, low fitness

Section 16-2

b. Stabilizing Selectionb. Stabilizing Selection

When individuals near the center of the When individuals near the center of the curve curve

have higher fitness than individuals at either have higher fitness than individuals at either endend

of the curveof the curve Key

Per

cen

tag

e o

f P

op

ula

tio

n

Birth Weight

Selection against both

extremes keep curve narrow and in same

place.

Low mortality, high fitness

High mortality, low fitness

Stabilizing Selection

c. Disruptive Selectionc. Disruptive Selection

When individuals at the upper and lower When individuals at the upper and lower ends ofends of

the curve have higher fitness than the curve have higher fitness than individuals individuals

near the middle.near the middle.

Largest and smallest seeds become more common.

Nu

mb

er o

f B

ird

sin

Po

pu

lati

on

Beak Size

Population splits into two subgroups specializing in different seeds.

Beak Size

Nu

mb

er o

f B

ird

sin

Po

pu

lati

on

Key

Low mortality, high fitness

High mortality, low fitness

3. Genetic Drift3. Genetic Drift – – Random changeRandom change in the in the frequency frequency

of a gene. (not natural selection) Occurs more in of a gene. (not natural selection) Occurs more in small small

population.population. a.a. Can happen by natural disasters – certain Can happen by natural disasters – certain

phenotypes in a population die and it then phenotypes in a population die and it then changes changes

the gene poolthe gene pool b. Founders effect – a group leaves a population and b. Founders effect – a group leaves a population and settles in new location after generations, new settles in new location after generations, new

looks different than original population. Chance – looks different than original population. Chance – not not

natural selection.natural selection.

Sample of Original Population

Founding Population A

Founding Population B

Descendants

Founding Population B

Notice the New populations look different than the original, because of the Random members that left and breed new populations

B. Evolution vs. Genetic EquilibriumB. Evolution vs. Genetic Equilibrium

a. Evolution is a change in allele frequenciesa. Evolution is a change in allele frequencies

b. b. Genetic EquilibriumGenetic Equilibrium – no genetic change. – no genetic change.

If allele freq do not change then pop will not If allele freq do not change then pop will not

evolve (look the same)evolve (look the same)

Galapagos Islands show an example of SLOW Galapagos Islands show an example of SLOW

change – more equilibriumchange – more equilibrium

c. c. Hardy-Weinberg PrincipleHardy-Weinberg Principle says…… says……

allele frequencies will remain constant unless one or allele frequencies will remain constant unless one or

more factors causes those frequencies to change. more factors causes those frequencies to change.

For genetic equilibrium to occurFor genetic equilibrium to occur(no evolution)(no evolution)

1. random mating1. random mating

2. population must be large2. population must be large

3. can be no migration or emigration3. can be no migration or emigration

4. no mutation4. no mutation

5. no natural selection5. no natural selection

What would happen if one of these thingsWhat would happen if one of these things

occurred/changed?occurred/changed?

The allele frequencies for a trait would change and The allele frequencies for a trait would change and

Evolution !!!!!!Evolution !!!!!!

Equation:Equation: pp22 + 2pq + q + 2pq + q2 2 = 1= 1Used to determine if the frequencies of alleles change in Used to determine if the frequencies of alleles change in

a population.a population.

PP22= homozygous dominant in pop= homozygous dominant in pop

2pq= heterozygous dominant in pop2pq= heterozygous dominant in pop

qq22 = recessive phenotype in pop = recessive phenotype in pop

p= frequency of dom allele in a pop p= frequency of dom allele in a pop

q= frequency of rec allele in a pop q= frequency of rec allele in a pop

p+q = 1 total allelesp+q = 1 total alleles

Example:Example:

If there are 50 people = 100 alleles (T, t)If there are 50 people = 100 alleles (T, t)

40 T alleles = 40 % = .4 = p40 T alleles = 40 % = .4 = p

60 t alleles = 60% = .6 = q60 t alleles = 60% = .6 = q

..4 + .6 = 1 (total alleles4 + .6 = 1 (total alleles))

pp22 + 2pq + q + 2pq + q2 2 = 1 p + q = 1 p = dom allele= 1 p + q = 1 p = dom allele

PTC Tasting is dominant q = rec allelePTC Tasting is dominant q = rec allele

ExampleExample:: 17 student: 12 tasters, 5 nontasters 17 student: 12 tasters, 5 nontasters

tasters (TT, Tt)= 12/17 = .7 = ptasters (TT, Tt)= 12/17 = .7 = p22 + 2pq + 2pq

non-tasters (tt) = 5/17= non-tasters (tt) = 5/17= .3 = q.3 = q22 so so q =.54 q =.54

p + q = 1 p + p + q = 1 p + .54.54= 1 p = .= 1 p = .46 (T)46 (T)

p2 = .p2 = .46 46 xx . .4646 = .2 = ………. 20 % TT tasters = .2 = ………. 20 % TT tasters

2pq = 2 2pq = 2 xx . .5454 x x ..4646 = .5 …….50% Tt tasters = .5 …….50% Tt tasters

q2 = .q2 = .5454 xx . .5454 = .3 = ………..30 % tt non-tasters = .3 = ………..30 % tt non-tasters

The point is, then…..if p & q change The point is, then…..if p & q change over time then the phenotype ratios over time then the phenotype ratios will change too = EVOLUTIONwill change too = EVOLUTION

Use HW at 2 points and compare the Use HW at 2 points and compare the p & q values to see if there is a shiftp & q values to see if there is a shift

16.3 Speciation: Evolution to the MAX16.3 Speciation: Evolution to the MAX

SpeciesSpecies : a group of similar organisms that : a group of similar organisms that breed produce fertile offspring in a natural breed produce fertile offspring in a natural environment.environment.

SpeciationSpeciation: new species evolving from old : new species evolving from old species.species.

When the gene pools change so much from the When the gene pools change so much from the

original, a new species develops.original, a new species develops.

Reproductive IsolationReproductive Isolation - - When members of a population can’t or don’t When members of a population can’t or don’t

reproduce….the gene pools become isolatedreproduce….the gene pools become isolated SpecificSpecific mating instead of mating instead of random random matingmating 3 kinds of Rep Isolation3 kinds of Rep Isolation

a. Behavioral isolationa. Behavioral isolation: different courtship rituals or : different courtship rituals or other other

types of mating behavior that prevent matingtypes of mating behavior that prevent mating

lacewing

b.b. Geographic isolationGeographic isolation: A pop is: A pop is

separated by geographic barriers – rivers, mountains, separated by geographic barriers – rivers, mountains,

other water.other water.

no random matingno random mating

now, but only within those now, but only within those

members that are together. members that are together.

Galapagos Islands = exampleGalapagos Islands = examplecalifornia salamanders

c.c. Temporal isolation: Temporal isolation: 2 or more2 or more

species reproduce at different times.species reproduce at different times.

Seasonal differences in matingSeasonal differences in mating

Example of speciation though a combination of factors: Example of speciation though a combination of factors: geographical, behavioral, niche changesgeographical, behavioral, niche changes

Chimps and bonobos Chimps and bonobos

diverge into 2 speciesdiverge into 2 species..

Chimps & Bonobos

Example of how there more than Example of how there more than

geographical isolation affects speciation.geographical isolation affects speciation.

environmental factors mold evolution too.environmental factors mold evolution too.

PBS Hummingbird

Section 16-3

results from

which include

produced by produced byproduced by

which result in

which result in

Reproductive Isolation

Isolating mechanisms

Behavioral isolation Temporal isolationGeographic isolation

Behavioral differences Different mating timesPhysical separation

Independentlyevolving populations

Formation ofnew species

Reproductive isolation leads to new species

Speciation in Darwin's Speciation in Darwin's FinchesFinches Speciation in Darwin's FinchesSpeciation in Darwin's Finches

– Speciation in the Galápagos finches Speciation in the Galápagos finches occurred by:occurred by: founding of a new populationfounding of a new population geographic isolationgeographic isolation changes in new population's gene changes in new population's gene poolpool

reproductive isolationreproductive isolation ecological competitionecological competition Continued evolutionContinued evolution

Speciation in Darwin's Speciation in Darwin's FinchesFinches

Founders Arrive Founders Arrive 

A few finches—species A—travel from South America to one of the Galápagos Islands.

There, they survive and reproduce.

Speciation in Darwin's Speciation in Darwin's FinchesFinches

– Geographic IsolationGeographic Isolation

Some birds from species A cross to a second island.

The two populations no longer share a gene pool.

Speciation in Darwin's Speciation in Darwin's FinchesFinches Changes in the Gene PoolChanges in the Gene Pool

Seed sizes on the second island favor birds with large beaks.

The population on the second island evolves into population B, with larger beaks.

Speciation in Darwin's Speciation in Darwin's FinchesFinches

– Reproductive IsolationReproductive Isolation If population If population BB birds cross back to the birds cross back to the

first island, they will not mate with first island, they will not mate with birds from population birds from population AA..

Populations Populations AA and and BB have become have become separate species.separate species.

Testing Natural SelectionTesting Natural Selection in Nature in Nature

Speciation in Darwin's Speciation in Darwin's FinchesFinches

– Ecological CompetitionEcological Competition As species As species AA and and BB compete for compete for

available seeds on the first island, available seeds on the first island, they continue to evolve in a way that they continue to evolve in a way that increases the differences between increases the differences between them. them.

A new speciesA new species——CC—may evolve.—may evolve.

Testing Natural SelectionTesting Natural Selection in Nature in Nature

Speciation in Darwin's Speciation in Darwin's FinchesFinches

– Continued EvolutionContinued Evolution This process of isolation, genetic This process of isolation, genetic

change, and reproductive isolation change, and reproductive isolation probably repeated itself often across probably repeated itself often across the entire Galápagos island chain.the entire Galápagos island chain.

Chapter 17 History of Chapter 17 History of LifeLife

17.1 Fossil Record17.1 Fossil Recorda. Shows change in organisms over timea. Shows change in organisms over time

b. Sedimentary rock forms layers, encasing any dead organisms b. Sedimentary rock forms layers, encasing any dead organisms

that have fallen into that layer. Older fossils are on bottom that have fallen into that layer. Older fossils are on bottom

rock layersrock layers

Pressure turns sediment into rock and many bones are preserved Pressure turns sediment into rock and many bones are preserved

by mineral saturation. by mineral saturation.

Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

Section 17-1

FossilizationFossilization

PBS FossilizationPBS Fossilization

Show how fossils are used to piece Show how fossils are used to piece

together the ancestry of whales from together the ancestry of whales from that of land mammals to aquatic that of land mammals to aquatic mammals.mammals.

Lucy fossilizationLucy fossilization

Show how fossils are formedShow how fossils are formed

Relative Dating

Can determine

Is performed by

Drawbacks

Absolute Dating

Comparing Relative and Absolute Dating of Fossils

Section 17-1

Compare/Contrast Table

Imprecision and limitations of age data

Difficulty of radioassay laboratory methods

Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock

Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen

Age of fossil with respect to another rock or fossil (that is, older or younger)

Age of a fossil in years

2 Ways of Determing the Age of Fossils

Carbon 14 is a radioactive isotope. Its half-life is 5730 Carbon 14 is a radioactive isotope. Its half-life is 5730 years. The amount of C14 left in a fossil sample can years. The amount of C14 left in a fossil sample can determine the determine the

age of the fossil.age of the fossil.

Radiometric dating PBSRadiometric dating PBS

17.2 Earth’s Early History17.2 Earth’s Early HistoryHypotheses about the beginning of earth and life are Hypotheses about the beginning of earth and life are

based on a based on a

small amount of scientific data. As new evidence is small amount of scientific data. As new evidence is found, found,

scientists ideas might change. Part of the process of scientists ideas might change. Part of the process of science is science is

Collecting data, evaluating, and revising!Collecting data, evaluating, and revising!

A. 1950’s Urey & Miller designed experiments to A. 1950’s Urey & Miller designed experiments to examine examine

how inorganic compounds how inorganic compounds

could from into organic could from into organic

molecules (proteins, DNA).molecules (proteins, DNA).

spark

Water vapor

Condensed amino acids

gases

* When a spark was added to their “soup” of * When a spark was added to their “soup” of chemicals, chemicals,

simple amino acids were formed.simple amino acids were formed.

* There were problems with the experiment, but * There were problems with the experiment, but more more

recent experiments have been able to produce recent experiments have been able to produce

cytosine and uracil which are in RNA.cytosine and uracil which are in RNA.

B. Which came first…DNA or RNA? B. Which came first…DNA or RNA?

Need DNA to make RNA and RNA Need DNA to make RNA and RNA

is easier to make…….is easier to make…….

Thought that pieces of RNA Thought that pieces of RNA

were produced first and helped in were produced first and helped in

the formation of DNA then proteins….the formation of DNA then proteins….

C. Simple prokaryotes formed first. Did not use oxygen. C. Simple prokaryotes formed first. Did not use oxygen. They They

became photosynthetic and oxygen levels began to became photosynthetic and oxygen levels began to rise in the rise in the

atmosphere.atmosphere.

D. How did Eukaryotes form? One thought is the D. How did Eukaryotes form? One thought is the EndosymbioticEndosymbiotic

Theory. Was not recognized as a viable theory until Theory. Was not recognized as a viable theory until the the

1960’s by Lynn Margulis. (Boston!)1960’s by Lynn Margulis. (Boston!)

Eukaryotic Cells developed from a symbiotic Eukaryotic Cells developed from a symbiotic relationship relationship

between several kinds of prokaryotes (bacteria) – between several kinds of prokaryotes (bacteria) – each had each had

its own “specialty” and together – formed a great its own “specialty” and together – formed a great “unit”“unit”

Aerobic bacteria

Ancient prokaryotic

Plant and Plantlike cells

Animals, fungus cells

mitochondrion

Photosynthetic bacteria

Primitive eukaryote

Nuclear envelope

Concept Map

Evolution of LifeSection 17-2

Early Earth was hot; atmosphere contained poisonous gases.

Earth cooled and oceans condensed.

Simple organic molecules may have formed in the oceans..

Small sequences of RNA may have formed and replicated.

First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.

Later prokaryotes were photosynthetic and produced oxygen.

An oxygenated atmosphere capped by the ozone layer protected Earth.

First eukaryotes may have been communities of prokaryotes.

Multicellular eukaryotes evolved.

Sexual reproduction increased genetic variability, hastening evolution.

4 billion

3.8 billion

2 billion

3.5 billion

500 mil

17.4 Patterns of Evolution17.4 Patterns of EvolutionMacroevolution – Macroevolution – Long term change (whole new orgnisms)Long term change (whole new orgnisms)

5 Patterns of Macroevolution5 Patterns of Macroevolution

1. 1. Extinction: large numbers of species disappear.Extinction: large numbers of species disappear. The result is the remaining species now have new The result is the remaining species now have new

niches (job)niches (job)

to fill, and may then thrive and evolve.to fill, and may then thrive and evolve.

Permian Extinction – PBSPermian Extinction – PBS

extinctionextinction

invasive species - extinctioninvasive species - extinction

2. . Adaptive Radiation: single species evolved 2. . Adaptive Radiation: single species evolved into several different species with different into several different species with different living habits.living habits.

3. 3. Convergent Evolution: is when adaptive Convergent Evolution: is when adaptive radiationradiation

produces two unrelated species that actually produces two unrelated species that actually appear appear

similar. similar.

Started out with completely different genetic Started out with completely different genetic material, material,

niches, and habitats. Over time, natural selection niches, and habitats. Over time, natural selection

molds similar body forms – analogous structuresmolds similar body forms – analogous structuresNot related but havesimilar body structuredue to the long periodof selection for thesetraits in separateenvironments

Convergent EvolutionConvergent Evolution PBS AnteaterPBS Anteater

4. Coevolution4. Coevolution

The evolution of two organisms together.The evolution of two organisms together.

The two organisms benefit each other The two organisms benefit each other and and

therefore they change togethertherefore they change together

Toxic NewtToxic Newt

LeafcutterLeafcutter

red queenred queen

allergies and asthmaallergies and asthma

5. Punctuated Equilibrium5. Punctuated EquilibriumThere is variation in the rate of evolutionThere is variation in the rate of evolution. . * There is evidence of a slow and gradual evolution * There is evidence of a slow and gradual evolution

(Darwin’s (Darwin’s big thing). Tortoises – state of slow equilibriumbig thing). Tortoises – state of slow equilibrium gradualism.gradualism.

* There is also evidence of bursts of rapid evolution in * There is also evidence of bursts of rapid evolution in which several new species have formed. (rapid is still which several new species have formed. (rapid is still thousands or millions of yearsthousands or millions of years. . Punctuated Punctuated

equilibriumequilibrium

Affects small populationsAffects small populationsmore dramatically. more dramatically. * isolation* isolation * migration* migration * extinction* extinction

Gradualism