Evolution A Scientific Explanation for Similarities and Differences Between Species.

EvolutionEvolution

A Scientific Explanation for A Scientific Explanation for Similarities and Differences Similarities and Differences Between SpeciesBetween Species

EvolutionEvolution

• Evolution = progressive change in Evolution = progressive change in characteristics of organisms as a characteristics of organisms as a result of changes in genetic result of changes in genetic compositioncomposition

• Two important aspects Two important aspects – Descent from a common ancestorDescent from a common ancestor– Adaptation to the environmentAdaptation to the environment

• Adaptation = characteristic that makes it Adaptation = characteristic that makes it more likely that an organism will survive more likely that an organism will survive and reproduce in its environmentand reproduce in its environment

A Flowchart of Evolutionary Reasoning

Potential forrapid reproduction

Relatively constantresources and

population over time

Variability instructures and

behaviors

Some variability is inherited; adaptations

increase in future generations

(observations)

(conclusions)

Competition for survival and reproduction (1)

NATURAL SELECTIONOn average, the fittest

organisms leavethe most offspring (2)

EVOLUTION:The genetic makeup of the

population changes over time, driven by natural selection (3)

Formation of new genotypes leads to

phenotypic variation

Struggle for existence

Survival of the fittest

Adaptation

Natural Selection As the Mechanism for Evolution

An increase in frequency of genotypes that confer a favorable advantage in a given environment.

Applying Your KnowledgeApplying Your Knowledge

A.A. The mechanism for evolution is The mechanism for evolution is B.B. A progressive change in the A progressive change in the

characteristics of organisms is characteristics of organisms is C.C. A trait that makes a species A trait that makes a species

survival more likely is called a(n)survival more likely is called a(n)

1.1. AdaptationAdaptation2.2. EvolutionEvolution3.3. Natural selectionNatural selection

Evidence for Common Descent From the Fossil RecordEvidence for Common Descent From the Fossil Record

Progressive changes from simpler to more complex Progressive changes from simpler to more complex organisms can be seen in the fossil record.organisms can be seen in the fossil record.

BiogeographicalBiogeographicalEvidence for Evidence for Common DescentCommon Descent

Different island species resemble each other.Different island species resemble each other.

Biogeographical Evidence for Biogeographical Evidence for Common DescentCommon Descent

Island Populations resemble Island Populations resemble those on nearby land.those on nearby land.

The Galapagos finches resembled the The Galapagos finches resembled the grassquit found on the coast of Ecuador.grassquit found on the coast of Ecuador.

Anatomical Evidence for Common Descent: Homologous Structures

FlyingFlying SwimmingSwimming RunningRunning GraspingGrasping

Anatomical Evidence:Anatomical Evidence: Vestigial Structures Vestigial Structures

Functional hindlimb Functional hindlimb in salamanderin salamander

Remnants of Remnants of hindlimb seen in hindlimb seen in boa and whaleboa and whale

Evidence for Common Descent Evidence for Common Descent from Biochemistryfrom Biochemistry

Evidence for Evolution from BiochemistryEvidence for Evolution from Biochemistry

Similarities in sequence measured by Similarities in sequence measured by ease of separating DNA strands by heat ease of separating DNA strands by heat

Evidence for Evolution: GeneticsEvidence for Evolution: Genetics

• Mutation generates diversityMutation generates diversity

• Meiosis and Fertilization generate new Meiosis and Fertilization generate new combinations due to combinations due to

– Crossing Over Crossing Over

– Alternate patterns of chromosome Alternate patterns of chromosome segregationsegregation

– Unique genotype of fertilizing sperm Unique genotype of fertilizing sperm combined with unique genotype of egg combined with unique genotype of egg

Two Types of Evolution Two Types of Evolution

Microevolution Microevolution

Macroevolution Macroevolution

Change within a Change within a population or species population or species

Change to a new Change to a new species species

Microevolution led to Microevolution led to an increase in dark-an increase in dark-winged Pepper Mothswinged Pepper Mothsin industrial regions of in industrial regions of Britain.Britain.

Evolution As a Change in Evolution As a Change in GenotypesGenotypes

GenotypeGenotype PhenotypePhenotype

SSSS No disease No disease Susceptible to MalariaSusceptible to Malaria

SS’SS’ Sickle Cell Trait (mild Sickle Cell Trait (mild symptoms)symptoms)Resistant to MalariaResistant to Malaria

S’S’S’S’ Sickle Cell Anemia Sickle Cell Anemia Die from anemiaDie from anemia

Individuals carrying the S’ allele were Individuals carrying the S’ allele were more likely to survive when malaria more likely to survive when malaria is the selecting agent.is the selecting agent.

Malaria as an Agent Malaria as an Agent of Natural Selectionof Natural Selection

S’S’S’S’

S’S’S’S’

SSSS

SSSS

SS’SS’

SS’SS’

SS’SS’

SSSS

S’S’S’S’

Malaria Malaria Eliminates SSEliminates SS

XX

XX

XXAnemia Anemia Eliminates S’S’Eliminates S’S’

XX

XX

XX

SS’SS’

SS’SS’

SS’SS’

RemainingRemainingGenotypesGenotypes

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

• A condition where A condition where allele frequenciesallele frequencies and and

genotypic frequenciesgenotypic frequencies remain constant remain constant from generation to generationfrom generation to generation

• Changes from equilibrium values are Changes from equilibrium values are used to determine if natural selection is used to determine if natural selection is occurringoccurring

Hardy-Weinberg EquilibriumHardy-Weinberg EquilibriumAllelic Allelic FrequenciesFrequencies

p + q = 1p + q = 1

p = frequency of dominant allele (eg. A)p = frequency of dominant allele (eg. A)

q = frequency of recessive allele (eg. a)q = frequency of recessive allele (eg. a)

Genotypic Genotypic FrequenciesFrequencies

pp22 + 2pq + q + 2pq + q22 = 1 = 1

pp22== freq. of homozygous dominants (AA) freq. of homozygous dominants (AA)

qq22= freq. of homozygous recessives (aa)= freq. of homozygous recessives (aa)

2pq = frequency of heterozygotes (Aa)2pq = frequency of heterozygotes (Aa)

ConditionsConditions Large population size Large population size

Random mating Random mating

No migrationNo migration

No mutationNo mutation

No selectionNo selection

Example Using Example Using Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

• If the frequency of albinos in a If the frequency of albinos in a population is 9%, what is the frequency population is 9%, what is the frequency of AA and Aa genotypes?of AA and Aa genotypes?

• Let A = allele for normal skin Let A = allele for normal skin pigmentationpigmentation

• Let a = allele for albinismLet a = allele for albinism

.7A

.3a

.7A .3a

.49AA .21Aa

.21Aa .09aa

0.09 q aa ofFrequency

0.42 2pq AaofFrequency

0.49p AA ofFrequency

2

2

0.7q1p

0.3q q

0.09q Albinosof Frequency2

2

Applying Hardy-Weinberg Equilibrium Applying Hardy-Weinberg Equilibrium Values to RFLP AnalysisValues to RFLP Analysis

Conditions of Hardy-Weinberg EquilibriumConditions of Hardy-Weinberg Equilibrium

ConditionCondition Non-equilibrium ConditionNon-equilibrium Condition

Large Large Population Population SizeSize

Genetic Drift: Changes in allele Genetic Drift: Changes in allele frequency due to small population sizesfrequency due to small population sizes

1. Founder effect1. Founder effect

2. Population Bottleneck 2. Population Bottleneck



Random Random MatingMating

Non-random mating: Alters genotypic Non-random mating: Alters genotypic but not allelic frequenciesbut not allelic frequencies



No MigrationNo Migration Migration: Can add new alleles, remove Migration: Can add new alleles, remove alleles or change allele frequencyalleles or change allele frequency

Leads to Gene Flow between populationsLeads to Gene Flow between populations



No MutationNo Mutation Mutation: Alters allele frequency, Mutation: Alters allele frequency, causes formation of new genotypescauses formation of new genotypes



No SelectionNo Selection Natural Selection: Increases frequency Natural Selection: Increases frequency of genotypes with higher fitnessof genotypes with higher fitness

Molecular EvolutionMolecular Evolution

Two Hypotheses for the Origin of Modern Humans

DNA Analyses DNA Analyses Related to Human OriginsRelated to Human Origins

Visit Visit http://www.http://www.dnalcdnalc.org/.org/ and choose and choose Genetic OriginsGenetic OriginsMitochondrial Control RegionMitochondrial Control RegionMedia and AnimationsMedia and AnimationsSolving the Mystery of the Solving the Mystery of the NeanderthalsNeanderthals

Other Applications of DNA Analysis Other Applications of DNA Analysis can be found at can be found at http://dnai.orghttp://dnai.org Choose ApplicationsChoose Applications

http://www.dnalc.org/



http://dnai.org/

Types of SelectionTypes of Selection

• Stabilizing: Stabilizing: eliminates extremeseliminates extremes


• Disruptive: Disruptive: increases both extremesincreases both extremes


• Directional: Directional: increases one extremeincreases one extreme


1.1. Stabilizing SelectionStabilizing Selection2.2. Disruptive SelectionDisruptive Selection3.3. Directional SelectionDirectional Selection

Which type of selection has occurred if Which type of selection has occurred if • The background is sandy with dark rocks The background is sandy with dark rocks

and snails are found with either dark or and snails are found with either dark or light shell colors?light shell colors?

• After spraying with malathion, more fruit After spraying with malathion, more fruit flies are found to be resistant to this flies are found to be resistant to this insecticide?insecticide?

Species FormationSpecies Formation

• Species = Group of actually or potentially Species = Group of actually or potentially interbreedinginterbreeding natural populations which natural populations which are are reproductively isolatedreproductively isolated from other from other such groupssuch groups

• Speciation depends onSpeciation depends on– isolation (lack of gene flow)isolation (lack of gene flow)– genetic divergencegenetic divergence

Mechanisms for SpeciationMechanisms for Speciation

• Allopatric SpeciationAllopatric Speciation– Occurs as a result of geographical isolationOccurs as a result of geographical isolation– Most common mechanismMost common mechanism

• Sympatric SpeciationSympatric Speciation– Occurs in the same locationOccurs in the same location– Can be due to ecological isolationCan be due to ecological isolation– Can be due to Polyploidy Can be due to Polyploidy

• Occurs for plants that have a sudden changeOccurs for plants that have a sudden change in numbers of chromosome sets in numbers of chromosome sets

Single species(white mice);homogeneous habitat

Geographical barrier(impassable river);isolated populations

Genetic drift;genetic divergence;

tan vs. white mice

Barrier removed(river dries up);

Mice mix but don’t interbreed.

Allopatric Speciation

(a)

(b)

(c)

(d)

Summary of Allopatric SpeciationSummary of Allopatric Speciation

• One group separates from the population.One group separates from the population.• Separate evolutionary pressures cause Separate evolutionary pressures cause

different genetic changes in both groups.different genetic changes in both groups. (Is this (1) microevolution or (2) macroevolution?)(Is this (1) microevolution or (2) macroevolution?)

• Sufficient genetic changes accumulate so Sufficient genetic changes accumulate so that interbreeding cannot occur if groups that interbreeding cannot occur if groups are rejoined. are rejoined.

(Is this (1) microevolution or (2) macroevolution?)(Is this (1) microevolution or (2) macroevolution?)

Sympatric Speciation

Single species(white mice);homogeneous habitat

(a)

Climate change;two habitats;isolated because don’t mix

(b)

Environmental pressure to adapt;genetic divergence;

tan vs. white mice

(c)

Sufficient divergence;

now different species

(d)

Speciation by Polyploidy

Chromosomes duplicatebut do not separateTetraploid with two sets of A and B.

Diploid with chromosome set A andchromosome set B.

Cross between diploid and tetraploid species Triploid with one each of chromosome sets A, B and D.

Chromosomes duplicate but do not separate Hexaploid with three sets of A, B and D.

Modern Wheat


A.A. Which process involves a sudden, large Which process involves a sudden, large change in chromosome number?change in chromosome number?

B.B. Which process requires geographical Which process requires geographical separation?separation?

C.C. Which process can occur as a result of small Which process can occur as a result of small differences within the same local environment? differences within the same local environment?

1.1. Sympatric SpeciationSympatric Speciation2.2. Speciation by PolyploidySpeciation by Polyploidy3.3. Allopatric Speciation Allopatric Speciation

Patterns of EvolutionPatterns of Evolution • DivergentDivergent

– different phenotypes arise as related different phenotypes arise as related species encounter environmental species encounter environmental differencesdifferences

Patterns of EvolutionPatterns of Evolution • ConvergentConvergent

– similar phenotypes arise in unrelated similar phenotypes arise in unrelated species as a result of environmental species as a result of environmental similaritiessimilarities

North AmericanNorth AmericanDesert Plants Desert Plants

CactusCactus

Euphorbs Euphorbs African African Desert Plants Desert Plants

Patterns of Evolution Patterns of Evolution

• Coevolution: Coevolution: species adjust together to species adjust together to maintain relationship maintain relationship

Flowering plants Flowering plants and their Pollinatorsand their Pollinators

Predators Predators and their Preyand their Prey

Evolution A Scientific Explanation for Similarities and Differences Between Species.

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