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.