Evolution of PopulationsEvolution of PopulationsChapter 16Chapter 16

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

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

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

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

Genes and VariationGenes and Variation

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

2 types of genetic drift2 types of genetic drift

Bottleneck effectBottleneck effect

Founder effectFounder effect

Bottleneck effectBottleneck effect

Genetic drift that occurs after an event Genetic drift that occurs after an event greatly reduces the size of the populationgreatly reduces the size of the population

Founder effectFounder effect

Genetic drift that occurs after a small Genetic drift that occurs after a small number of individuals colonize a new number of individuals colonize a new areaarea

Effects of genetic drift Effects of genetic drift

Population loses genetic variationPopulation loses genetic variation

Lethal alleles may become more Lethal alleles may become more commoncommon

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 chance of No Natural Selection: equal chance of survivalsurvival

Hardy-Weinberg EquationHardy-Weinberg Equation(p + q)(p + q)22 = 1, which is the same as = 1, which is the same as

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

p = frequency of “A” allele and p = frequency of “A” allele and q = frequency of “a” alleleq = frequency of “a” allele

pp22 = expected freq. of homozygotes for = expected freq. of homozygotes for one alleleone allele2pq = expected freq. of heterozygotes2pq = expected freq. of heterozygotesqq22 = expected freq. of homozygotes for = expected freq. of homozygotes for the other allelethe other allele

Hardy-Weinberg equilibriumHardy-Weinberg equilibrium

True of populations that are NOT True of populations that are NOT evolving… does that happen often?evolving… does that happen often?

CrashCourse

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

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

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.

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

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

ExtinctionExtinction

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

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

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)

CoevolutionCoevolution

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

Typical of plant-pollinator Typical of plant-pollinator relationshipsrelationships

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

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

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

Process of SpeciationProcess of Speciation

4 Main Isolating Mechanisms 4 Main Isolating Mechanisms

A.A. ReproductiveReproductive

B.B. BehavioralBehavioral

C.C. GeographicGeographic

D.D. TemporalTemporal

A. A. Reproductive IsolationReproductive Isolation: Two populations : Two populations cannot interbred and produce fertile offspringcannot interbred and produce fertile offspring

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

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

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

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

Sources of genetic variation:Sources of genetic variation:1.1. Mutations- change in DNA sequenceMutations- change in DNA sequence

2.2. Gene Shuffling- random assortment of genes Gene Shuffling- random assortment of genes during gamete production (SEXUAL during gamete production (SEXUAL reproduction)reproduction)

Gene Expression VariationGene Expression Variation Single-gene trait- controlled by one geneSingle-gene trait- controlled by one gene

Ex: Widow’s PeakEx: Widow’s Peak

Polygenic trait- controlled by many genesPolygenic trait- controlled by many genes Skin color, eye colorSkin color, eye color

Genes and VariationGenes and Variation

Original Source of Genetic Original Source of Genetic Variation?Variation?

MUTATION!MUTATION!

the evolution of sexual reproduction the evolution of sexual reproduction increased genetic diversity within a increased genetic diversity within a population and therefore accelerated the population and therefore accelerated the rate of evolutionrate of evolution