Evolution of PopulationsEvolution of PopulationsChapter 11Chapter 11

Warm Up 1/30 & 1/31Warm Up 1/30 & 1/31

1.1. Explain how the terms Explain how the terms traittrait, , genegene, and , and alleleallele are related. are related.

2.2. What is genetic drift and what types of What is genetic drift and what types of populations are affected?populations are affected?

3.3. Give an example of an isolating Give an example of an isolating mechanism which could result in mechanism which could result in speciation.speciation.

KEY CONCEPT KEY CONCEPT A population shares a A population shares a

common common gene poolgene pool

Gene pool - Gene pool - all the genes that all the genes that exist within a populationexist within a population

Genes and VariationGenes and Variation

Genetic variation Genetic variation in a population increases in a population increases the chance that some individuals will the chance that some individuals will

survivesurviveGenetic variation leads to phenotypic variation.Genetic variation leads to phenotypic variation.

Phenotypic variation is necessary for natural selection.Phenotypic variation is necessary for natural selection.

Genetic variation is stored in Genetic variation is stored in a populationa population’’s gene pool.s gene pool. made up of all alleles in a populationmade up of all alleles in a population allele combinations form when organisms have allele combinations form when organisms have

offspringoffspring

Relative (allelic) frequency Relative (allelic) frequency - the percentage of - the percentage of a particular allele in a gene pool. a particular allele in a gene pool.

Genes and VariationGenes and Variation

KEY CONCEPT KEY CONCEPT Populations, not individuals, evolve.Populations, not individuals, evolve.

Natural Selection in PopulationsNatural Selection in Populations

Natural Selection-Natural Selection- In nature, unequal ability In nature, unequal ability to survive and reproduce... Survival of the to survive and reproduce... Survival of the fittest. fittest.

Natural Selection ACTS ON Natural Selection ACTS ON PHENOTYPE but influences PHENOTYPE but influences

genotype (thus, allelic frequency)genotype (thus, allelic frequency)Artificial Selection- Artificial Selection- Mankind selects for Mankind selects for desired traits. Also known as “selective desired traits. Also known as “selective breeding”breeding”

Artificial SelectionArtificial Selection

Over time, the zebra herd becomes faster as Over time, the zebra herd becomes faster as the slower zebra (and their genes) are the slower zebra (and their genes) are

removed from the population… survival of removed from the population… survival of the fittestthe fittest

Darwin’s Theory = Evolution by means of Darwin’s Theory = Evolution by means of natural selectionnatural selection

ADAPT OR DIE!ADAPT OR DIE!Camouflage-Camouflage- organisms blend-in organisms blend-in

with surrounding environment with surrounding environment

Mimicry-Mimicry- species copy another to species copy another to insure their own survivalinsure their own survival

NatGeo

Natural Selection has three Natural Selection has three affects on affects on phenotype phenotype distributiondistribution

1.1.Directional SelectionDirectional Selection

2.2.Stabilizing SelectionStabilizing Selection

3.3.Disruptive SelectionDisruptive Selection

Natural Selection effects Genetic Natural Selection effects Genetic Change in PopulationsChange in Populations

Normal Distribution of traitsNormal Distribution of traits

A normal distribution graphs as a bell-A normal distribution graphs as a bell-shaped curve.shaped curve.

Phenotypes near thePhenotypes near the

middle range tend to middle range tend to

be most common.be most common.

Examples- height andExamples- height and

weightweight

Directional SelectionDirectional Selection

This type of selection favors phenotypes at This type of selection favors phenotypes at

one extreme of a trait’s range.one extreme of a trait’s range.

An extreme phenotype that was once rare An extreme phenotype that was once rare becomes more common.becomes more common.

Ex. Drug resistant bacteriaEx. Drug resistant bacteria

1.1. Directional Selection- Directional Selection- Individuals on one end Individuals on one end of a curve are “better of a curve are “better fitted” than the middle fitted” than the middle or other endor other end

Peccaries naturally choose to consume thosePeccaries naturally choose to consume those

cactus plants with the fewest spinescactus plants with the fewest spines As a result,As a result,

at flowering time there are more cacti withat flowering time there are more cacti with

higher spine numbers; thus, there are more ofhigher spine numbers; thus, there are more of

their alleles going into pollen, eggs, and seedstheir alleles going into pollen, eggs, and seeds

for the next generation.for the next generation.

Directional SelectionDirectional Selection

Stabilizing SelectionStabilizing Selection

Stabilizing selection favors the intermediate Stabilizing selection favors the intermediate phenotype.phenotype.

Selection against both extremes Selection against both extremes decreases the genetic diversity of a given decreases the genetic diversity of a given population.population.

Stabilizing SelectionStabilizing Selection

2.2. Stabilizing Selection- Stabilizing Selection- Individuals near center Individuals near center of a curve are “better of a curve are “better fitted” (have highest fitted” (have highest fitness) than both endsfitness) than both ends

Peccaries are consuming the low-spinePeccaries are consuming the low-spine

number plants, and the insects are killingnumber plants, and the insects are killing

the high-spine-number plants. As thesethe high-spine-number plants. As these

gene combinations are removed from thegene combinations are removed from the

cactus gene pool, there is less and lesscactus gene pool, there is less and less

variety possible in subsequentvariety possible in subsequent

generations. generations.

Disruptive SelectionDisruptive Selection

This type of selection occurs when This type of selection occurs when bothboth extreme phenotypes are observed.extreme phenotypes are observed.

Individuals with the intermediate type are Individuals with the intermediate type are selected against.selected against.

By favoring both extreme phenotypes, By favoring both extreme phenotypes, disruptive selection can lead to the disruptive selection can lead to the formation of a new species.formation of a new species.

3.3. Disruptive Selection- Disruptive Selection- Individuals at upper and Individuals at upper and lower ends are “better fitted” lower ends are “better fitted” than the ones in the middlethan the ones in the middle

Years of collecting have left their toll onYears of collecting have left their toll on

the roadside cacti. In this environment, it isthe roadside cacti. In this environment, it is

maladaptive to be good looking and havemaladaptive to be good looking and have

a reasonable number of spines. Low a reasonable number of spines. Low

spine-number plants are not pickedspine-number plants are not picked

because they don't "look right", and highbecause they don't "look right", and high

spine-number varieties are left alonespine-number varieties are left alone

because they are too hard to pick.because they are too hard to pick.

Gradually, the gene pool changes in favorGradually, the gene pool changes in favor

of the two extreme spine number types.of the two extreme spine number types.

Disruptive SelectionDisruptive Selection

Other mechanisms of EvolutionOther mechanisms of Evolution

Natural selection is not the only Natural selection is not the only mechanism through which populations mechanism through which populations evolveevolve

3 other mechanisms of Evolution:3 other mechanisms of Evolution:

Gene FlowGene Flow

Genetic DriftGenetic Drift

Sexual SelectionSexual Selection

Gene flow – Gene flow – movement of alleles into movement of alleles into or out of a populationor out of a population

Immigration – new alleles move INImmigration – new alleles move IN

Emigration – alleles move OUTEmigration – alleles move OUT

Genetic drift Genetic drift - change - change in allelic frequencies in allelic frequencies by chanceby chance

Ex: sudden extinction of Ex: sudden extinction of a dominant species; a dominant species; small populations small populations most affectedmost affected

Genetic drift is a change in allele frequencies due to Genetic drift is a change in allele frequencies due to

chancechance. .

Genetic drift causes a loss of genetic diversity Genetic drift causes a loss of genetic diversity It is most common in small populations.It is most common in small populations.

A population bottleneck can lead to genetic A population bottleneck can lead to genetic drift. drift. It occurs when an eventIt occurs when an event

drastically reducesdrastically reducespopulation size.population size.

The bottleneck effect isThe bottleneck effect isgenetic drift that occursgenetic drift that occursafter a bottleneck event.after a bottleneck event.

The founding of a small population can The founding of a small population can lead to genetic drift.lead to genetic drift.– It occurs when a few individuals start a new It occurs when a few individuals start a new

population.population.– The The founder effectfounder effect is genetic drift that occurs is genetic drift that occurs

after start of new populationafter start of new population

Sexual selection Sexual selection occurs when certain traits occurs when certain traits

increase mating successincrease mating success. . Sexual selection occurs due to higher cost of Sexual selection occurs due to higher cost of reproduction for females.reproduction for females. males produce many sperm continuouslymales produce many sperm continuously females are more limited in potential offspring each females are more limited in potential offspring each

cyclecycle

Genetic equilibrium Genetic equilibrium - when alleles stay the same - when alleles stay the same from generation to generationfrom generation to generation

The Hardy Weinberg Principle: Allele The Hardy Weinberg Principle: Allele frequencies will remain constant under five frequencies will remain constant under five conditionsconditions

1.1. Random MatingRandom Mating

2.2. Large PopulationLarge Population

3.3. No movement (immigration or emigration)No movement (immigration or emigration)

4.4. No MutationsNo Mutations

5.5. No Natural Selection: equal change of No Natural Selection: equal change of survivalsurvival

5 Factors that can lead to 5 Factors that can lead to evolutionevolution

Genetic DriftGenetic Drift

Gene FlowGene Flow

MutationMutation

Sexual SelectionSexual Selection

Natural SelectionNatural Selection

Genetic drift Genetic drift changes allele frequencies changes allele frequencies due to chance alonedue to chance alone

Gene flow Gene flow moves alleles from moves alleles from one population to anotherone population to another

MutationsMutations produce the genetic variation produce the genetic variation needed for evolution. needed for evolution.

Sexual selection Sexual selection selects for traits that selects for traits that improve mating success.improve mating success.

Natural selectionNatural selection selects for traits selects for traits advantageous for survivaladvantageous for survival

KEY CONCEPT KEY CONCEPT New species can arise when populations New species can arise when populations

are isolatedare isolatedThe isolation of populations can lead to speciationThe isolation of populations can lead to speciation

speciationspeciation - evolution of a new species - evolution of a new species

. .

Reproductive isolation can occur between isolated Reproductive isolation can occur between isolated populationspopulations

Populations can become isolated in several ways:Populations can become isolated in several ways: 1. 1. BehavioralBehavioral 2. 2. GeographicGeographic 3. 3. TemporalTemporal

1. 1. Behavioral IsolationBehavioral Isolation: Two populations : Two populations capable of breeding but cannot because of capable of breeding but cannot because of courtship ritualscourtship rituals

2. 2. Geographic IsolationGeographic Isolation: Two populations are : Two populations are separated by geographic barriersseparated by geographic barriers

Ex: Rivers, Oceans, MountainsEx: Rivers, Oceans, Mountains

3. 3. Temporal IsolationTemporal Isolation: Two or more : Two or more populations reproduce at different times populations reproduce at different times

Patterns of EvolutionPatterns of Evolution

1.1. ExtinctionExtinction

2.2. Divergent Evolution (adaptive radiation)Divergent Evolution (adaptive radiation)

3.3. Convergent EvolutionConvergent Evolution

4.4. CoevolutionCoevolution

1.Extinction1.Extinction

Why do species go extinct?Why do species go extinct?

ExtinctionExtinction

Natural selection, climate Natural selection, climate changes, and changes, and catastrophic events have catastrophic events have caused 99 percent of all caused 99 percent of all species that have ever species that have ever lived to become extinct.lived to become extinct.

Mass extinctionsMass extinctions – – caused by continents caused by continents moving, sea level moving, sea level changing, volcano changing, volcano eruptions, large meteorseruptions, large meteors

CatastrophicEvent

CatastrophicEvent

Predict what each ecosystem will look like after the event.Predict what each ecosystem will look like after the event.

QuestionQuestion

When a mass extinction happens, what do When a mass extinction happens, what do you think will happen next?you think will happen next?

Divergent Evolution Divergent Evolution (adaptive radiation)(adaptive radiation)

Divergent evolutionDivergent evolution – natural selection – natural selection causes 1 species to evolve into many causes 1 species to evolve into many species with many different adaptations species with many different adaptations (homologous structures)(homologous structures)

After mass extinctions, many environments will After mass extinctions, many environments will be open for inhabitationbe open for inhabitation

Species will migrate to that area and new Species will migrate to that area and new environmental pressures will cause the environmental pressures will cause the population to change over timepopulation to change over time

This is also known as This is also known as Adaptive RadiationAdaptive Radiation

Adaptive Radiation in Adaptive Radiation in honeycreepershoneycreepers

Homologous structures Homologous structures - similar structures - similar structures found in related organisms that are adapted found in related organisms that are adapted for different purposes. for different purposes.

Ex: human arm and bat wing or whale flipperEx: human arm and bat wing or whale flipper

---DIVERGENT EVOLUTION------DIVERGENT EVOLUTION---the process of two or more related species becoming

more and more dissimilar.

Evidence of EvolutionEvidence of Evolution

Homologous structures Homologous structures Divergent evolutionDivergent evolution

Convergent EvolutionConvergent Evolution

Convergent EvolutionConvergent Evolution – when unrelated – when unrelated organisms come to resemble one another organisms come to resemble one another (analagous structures)(analagous structures)

Analogous structures Analogous structures - structures found - structures found in unrelated organisms that have a similar in unrelated organisms that have a similar function but may be structurally differentfunction but may be structurally different

Ex: bird wing and insect wingEx: bird wing and insect wing

---CONVERGENT EVOLUTION------CONVERGENT EVOLUTION---

independent evolution of similar features in species of different

lineages

Analogous structures Analogous structures Convergent evolutionConvergent evolution

CoevolutionCoevolution

When 2 species When 2 species evolve in response to evolve in response to one anotherone another

CoevolutionCoevolution can occur in competitive can occur in competitive relationships, sometimes called relationships, sometimes called

evolutionary.evolutionary.

Speciation occurs in patternsSpeciation occurs in patterns

Punctuated equilibrium: species show little Punctuated equilibrium: species show little evolutionary change for millions of years, evolutionary change for millions of years, followed by periods of rapid speciationfollowed by periods of rapid speciation

Gradualism- Species evolve slowly, over Gradualism- Species evolve slowly, over long periods of time.long periods of time.