Chapter 16Chapter 16

Population Genetics and SpeciationPopulation Genetics and Speciation

Mrs. StewartMrs. Stewart

Honors BiologyHonors Biology

Central Magnet SchoolCentral Magnet School

Bell Work

List the evidence (at least 3) that supports the theory of evolution.

Standard / ObjectiveStandard / Objective

CLE 3210.5.3 CLE 3210.5.3 Explain how genetic Explain how genetic variation in a population and variation in a population and changing environmental conditions changing environmental conditions are associated with adaptation and are associated with adaptation and the emergence of new species.the emergence of new species.

Variation of Traits Within a Variation of Traits Within a PopulationPopulation

Variations in the genotypes of a population arise Variations in the genotypes of a population arise by:by:

mutationmutation – changes in genes that occur either – changes in genes that occur either naturally or influenced by environment naturally or influenced by environment

Passed to offspring if occurs in gametesPassed to offspring if occurs in gametes RecombinationRecombination – reshuffling of alleles – reshuffling of alleles

(chromosomes) and crossing over during (chromosomes) and crossing over during meiosis meiosis

random pairing of gametes random pairing of gametes – organisms – organisms produce large numbers of gametes, so the union produce large numbers of gametes, so the union of a particular pair is strictly by chance.of a particular pair is strictly by chance.

The Gene PoolThe Gene Pool The total genetic information available in a The total genetic information available in a

population is called the population is called the gene pool.gene pool.

Allele FrequencyAllele Frequency

Allele frequencyAllele frequency is is the number of times the number of times an allele occurs in an allele occurs in the gene pool the gene pool

This is in This is in comparison to how comparison to how often the other often the other alleles occur tooalleles occur too

Relative Allele FrequenciesRelative Allele Frequencies

determined by dividing the total number of a determined by dividing the total number of a certain allele by the total number of alleles of certain allele by the total number of alleles of all types in the populationall types in the population

Expressed as a percentage or a decimal. Expressed as a percentage or a decimal.

Example: I doExample: I doB = Blackb = brown

What are the allele frequencies?

B = 20 b = 30Total = 50

B = 20/50 = .40 or 40%b = 30/50 = .60 or 60%

Example: We do Example: We do

How many B? _________How many b? _________Total # of alleles for fur color? _________________

B = blackb = white

12

8

20

What is the allele frequency of B?

What is the allele frequency of b?

.60

.40

Example: You do Example: You do

Half of the population of four o’clocks has red Half of the population of four o’clocks has red flowers, and half has white flowers. What is flowers, and half has white flowers. What is the frequency of “r” allele?the frequency of “r” allele?

Predicting PhenotypePredicting Phenotype

Phenotype frequency is equal to the number Phenotype frequency is equal to the number of individuals with a particular phenotype of individuals with a particular phenotype divided by the total number of individuals in divided by the total number of individuals in the populationthe population..

Phenotype FrequencyPhenotype Frequency

Evolution is any change in the Evolution is any change in the relative frequency of alleles relative frequency of alleles in a in a population.population.

PopulationsPopulations, not individual , not individual organisms, can evolve over time.organisms, can evolve over time.

Hardy Weinberg Genetic Hardy Weinberg Genetic EquilibriumEquilibrium

Due to sexual reproduction, phenotypic Due to sexual reproduction, phenotypic frequencies may change over time. frequencies may change over time.

Does that mean the allele frequencies change Does that mean the allele frequencies change too?too?

Unless acted upon by an outside force Unless acted upon by an outside force (perhaps a changing environment), the answer (perhaps a changing environment), the answer is no. is no.

The Hardy-Weinberg Genetic The Hardy-Weinberg Genetic EquilibriumEquilibrium

Allele frequencies in the gene pool do not Allele frequencies in the gene pool do not change unless acted upon by certain forces.change unless acted upon by certain forces.

Hardy-Weinberg genetic equilibriumHardy-Weinberg genetic equilibrium is a is a theoretical model of a population in which no theoretical model of a population in which no evolution occurs and the gene pool of the evolution occurs and the gene pool of the population is stable.population is stable.

What factors affect the allele What factors affect the allele frequencies in a gene pool?frequencies in a gene pool?

Factors to keep H.W. equilibrium:Factors to keep H.W. equilibrium:

1.1. Lack of mutationsLack of mutations

2.2. No immigration or emigrationNo immigration or emigration

3.3. Ideally large population sizeIdeally large population size

4.4. Individuals mate randomlyIndividuals mate randomly

5.5. Selection does not occurSelection does not occur

Calculating using the Hardy Calculating using the Hardy Weinberg equationWeinberg equation

Dominant allele frequency = pDominant allele frequency = p Recessive allele frequency = qRecessive allele frequency = q p + q = 1p + q = 1 pp22 +2pq+ q +2pq+ q22 = 1 = 1

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Final question: Final question: How does immigration or How does immigration or emigration affect allele frequencies in a gene emigration affect allele frequencies in a gene pool?pool?

DarwinDarwin’’s s FinchesFinches

http://people.rit.edu/rhrsbi/GalapagosPages/Pictures/LandBirds/FinchTypes.jpeg

http://www.biology-online.org/images/darwin_finches.jpg

Five conditions under which Five conditions under which evolution may take placeevolution may take place

Genetic mutationsGenetic mutations Gene flowGene flow Genetic driftGenetic drift Nonrandom matingNonrandom mating Natural selection.Natural selection.

MutationMutation

MutationsMutations are changes in the DNA. are changes in the DNA.

Gene FlowGene Flow

EmigrationEmigration and and immigrationimmigration cause cause gene flowgene flow between populations and between populations and can thus affect gene frequencies.can thus affect gene frequencies.

Genetic DriftGenetic Drift

Genetic driftGenetic drift is a change in allele is a change in allele frequencies due to random events.frequencies due to random events.

Genetic drift operates most strongly Genetic drift operates most strongly in small populations.in small populations.

Nonrandom MatingNonrandom Mating

Mating is nonrandom whenever Mating is nonrandom whenever individuals may choose partnersindividuals may choose partners .. Sexual selectionSexual selection occurs when certain traits occurs when certain traits

increase an individualincrease an individual’’s success at mating. s success at mating. Sexual selection explains the development Sexual selection explains the development

of traits that improve reproductive success of traits that improve reproductive success but that may harm the individual.but that may harm the individual.

Natural SelectionNatural Selection

Three general patternsThree general patterns Stabilizing SelectionStabilizing Selection

favors the formation of average traits. favors the formation of average traits. Disruptive SelectionDisruptive Selection

favors extreme traits rather than average traits.favors extreme traits rather than average traits. Directional SelectionDirectional Selection

favors the formation of more-extreme traits.favors the formation of more-extreme traits.

The Concept of SpeciesThe Concept of Species

Biological species conceptBiological species concept a species is a population of organisms a species is a population of organisms

that can successfully interbreed but that can successfully interbreed but cannot breed with other groupscannot breed with other groups

Isolation and SpeciationIsolation and Speciation

Geographic IsolationGeographic Isolation Results from the separation of population subgroups by Results from the separation of population subgroups by

geographic barriers.geographic barriers. Allopatric SpeciationAllopatric Speciation

Speciation due to separation of subgroups of a populationSpeciation due to separation of subgroups of a population Reproductive IsolationReproductive Isolation

Results from the separation of population subgroups by Results from the separation of population subgroups by barriers to successful breeding.barriers to successful breeding.

Sympatric SpeciationSympatric Speciation Reproductive isolation within the same geographic areaReproductive isolation within the same geographic area

Allopatry vs SympatryAllopatry vs Sympatry

http://scienceblogs.com/evolvingthoughts/allopatry.jpg

http://deltabiology.com/wp-content/uploads/2012/02/Sympatry.jpg

Reproductive isolation: Reproductive isolation: MonkeyflowerMonkeyflower

http://faculty.washington.edu/toby/images/mim29%20Nature.jpg

Reproductive isolationReproductive isolation

http://evolution.berkeley.edu/evolibrary/images/evo/drosophila_scene7.gif

Rates of SpeciationRates of Speciation

GradualismGradualism species undergo small changes at a constant rate. species undergo small changes at a constant rate.

Punctuated equilibriumPunctuated equilibrium new species arise abruptly, differ greatly from new species arise abruptly, differ greatly from

their ancestors, and then change little over long their ancestors, and then change little over long periods.periods.