Population GeneticsPopulation Genetics

Population GeneticsPopulation Genetics• The sciencescience of genetic changegenetic change in

population.

• Remember:Remember: Hardy-Weinberg equation.– p² + 2pq + q² = 1 – p = frequency of dominant allele– q = frequency of recessive allele– Example:

• http://anthro.palomar.edu/synthetic/sample.htm

PopulationPopulation

• A localized group of individualsindividuals belonging to the same speciessame species.

SpeciesSpecies

• A group of populationspopulations whose individualsindividuals have the potential to interbreedinterbreed and produce viableviable offspring.

Gene PoolGene Pool

• The total collection of genescollection of genes in a population at any one time.

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• The conceptconcept that the shuffling of genesshuffling of genes that occurs during sexual reproduction, by itself, cannot changecannot change the overall genetic makeup of a population.

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• This principleprinciple will be maintained in nature only if all fivefive of the following conditions are met:

1.1. Very large populationVery large population

2.2. Isolation from other populationsIsolation from other populations

3.3. No net mutationsNo net mutations

4.4. Random matingRandom mating

5.5. No natural selectionNo natural selection

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• Remember:Remember:

If these conditions are met, the population is at equilibriumequilibrium.

• This means “No Change” or “No “No Change” or “No Evolution”.Evolution”.

MacroevolutionMacroevolution

• The origin of taxonomic groups higher higher than the species levelthan the species level.

MicroevolutionMicroevolution

• A change in a population’s gene poolpopulation’s gene pool over a secession of generations.

• Evolutionary changesEvolutionary changes in species over relatively brief periods of geological timegeological time.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

1. Genetic drift:1. Genetic drift:

Change in the gene pool of a Change in the gene pool of a small small population due to chance.population due to chance.

• Two examples:Two examples:

a. Bottleneck effecta. Bottleneck effect

b. Founder effectb. Founder effect

a. Bottleneck Effecta. Bottleneck Effect

• Genetic driftGenetic drift (reduction of alleles in a population) resulting from a disasterdisaster that drastically reduces reduces population sizepopulation size.

• Examples:Examples:

1.1. EarthquakesEarthquakes

2.2. Volcanic eruptionsVolcanic eruptions

b. Founder Effectb. Founder Effect

• Genetic driftGenetic drift resulting from the colonizationcolonization of a new location by a small number of individuals.

• Results in random changerandom change of the gene pool.

• Example:Example:

1.1. Islands (first Darwin’s finch)Islands (first Darwin’s finch)

• Simple illustration of founder effect. The original population is on the left with three possible

founder populations on the right.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

2. Gene Flow:2. Gene Flow:

TThe gain or loss of allelesgain or loss of alleles from a population by the movementmovement of individuals or gametes.

• Immigration or emigrationImmigration or emigration.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

3. Mutation:3. Mutation:

Change in an organism’s DNA thatChange in an organism’s DNA thatcreates a new allele.creates a new allele.

4. Non-random mating:4. Non-random mating:

The selection of mates other thanThe selection of mates other thanby chance.by chance.

5. Natural selection:5. Natural selection:

Differential reproduction.Differential reproduction.

Modes of ActionModes of Action

• Natural selectionNatural selection has three modesthree modes of action:

1.1. Stabilizing selectionStabilizing selection

2.2. Directional selectionDirectional selection

3.3. Diversifying selectionDiversifying selection

Number ofIndividuals

Size of individualsSmall Large

1.1. Stabilizing SelectionStabilizing Selection

• ActsActs upon extremesextremes and favorsfavors the intermediateintermediate.

Number ofIndividuals

Size of individualsSmall Large

2.2. Directional SelectionDirectional Selection

• FavorsFavors variants of one extremeone extreme.

Number ofIndividuals

Size of individualsSmall Large

3.3. Diversifying SelectionDiversifying Selection

• FavorsFavors variants of opposite extremesopposite extremes.

Number ofIndividuals

Size of individualsSmall Large

SpeciationSpeciation

• The evolutionevolution of new species.

Reproductive BarriersReproductive Barriers

• Any mechanismmechanism that impedesimpedes two species from producing fertile and/or viable hybrid fertile and/or viable hybrid offspringoffspring.

• Two barriers:Two barriers:

1.1. Pre-zygotic barriersPre-zygotic barriers

2.2. Post-zygotic barriersPost-zygotic barriers

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Artificial SelectionArtificial Selection

• The selective breedingselective breeding of domesticated plants and animals by man.

• Question:Question:

What’s the ancestor of the domesticated dog?

• Answer:Answer: WOLFWOLF

Evidence of EvolutionEvidence of Evolution

1.1. Biogeography: Biogeography:

Geographical distribution of species.Geographical distribution of species.

2. Fossil Record:2. Fossil Record:

Fossils and the order in which they Fossils and the order in which they appear appear in layers of sedimentary rock in layers of sedimentary rock (strongest (strongest evidence).evidence).

Evidence of EvolutionEvidence of Evolution

3. Taxonomy:3. Taxonomy:

Classification of life forms.Classification of life forms.

4. Homologous structures:4. Homologous structures:Structures that are similar because Structures that are similar because

of of common ancestry common ancestry (comparative (comparative anatomy)anatomy)

Evidence of EvolutionEvidence of Evolution

5. Comparative embryology:5. Comparative embryology:

Study of structures that appear Study of structures that appear during during embryonic development.embryonic development.

6. Molecular biology:6. Molecular biology:

DNA and proteins (amino acids)DNA and proteins (amino acids)