Genes and Variation

Population GeneticsChapter 16 & 17VocabularyPopulation- a group of individuals living in the same area that breed with each other.

Gene PoolGene pool- combination of genetic information from all of the individuals in the population.

What is Genetic Variation?Differences in alleles of genesProvides the raw material for natural selection

Genetic variation occurs among populations

Sources of Genetic VariationMutations-Changes in the DNA of the individualIf the mutation effects the individuals fitness it will effect the gene pool of the populationGene Shuffling- Occurs during the production of gametes Each chromosome moves independently during meiosis Crossing over

Relative FrequencyThe number of times that an allele occurs in the gene pool.Relative frequency has nothing to do with dominant and recessiveEvolution involves changes in populations over time

3020What is EvolutionHow is Evolution measured?Any change over time in the relative frequencies of alleles in a populationIt is populations not individual organisms that can evolve over time

Allele frequencies/ Gene pool

Change in relative frequency= evolution8Single Gene vs. Polygenic TraitsThe number of phenotypes produced is based on the number of genes that control the trait

Controlled by 1 geneproduces 2 phenotypesTraits that are controlled by 2 or more genesmore than 2 alleles for each traitNatural Selection on Single-gene traitsIndividuals either live or die based on their phenotypeA normally brown population of lizards experiences mutations that produce red and black lizardsWhat will happen to the population?What if the red lizards stand out more?What if the black lizards have an advantage over all other lizards?

Natural Selection on Single-gene traits

What do you expect the lizard population will look like by generation 50? Explain

Natural Selection on polygenic traitsWhen fitness varies natural selection can act

Three different ways that natural selection can affect the distribution of phenotypesDirectional SelectionStabilizing SelectionDisruptive Selection

Directional Selection

What would cause this shift?When individuals at one end of the curve have higher fitnessThe range of phenotypes shifts as individuals fail to survive/reproduce

Stabilizing Selection

What causes the shift?When individuals near the center of the curve have higher fitness then either end

Disruptive Selection

What would cause the shift?When individuals at either end of the curve have higher fitness then individuals near the middleNatural selection works hardest on the intermediate type

Genetic DriftGenetic Drift the random change in allele frequencies based on chanceSome individuals reproduce more times then othersLeave behind more offspringHas nothing to do with natural selection

Genetic DriftRelative frequencies move towards those that reproduce more times in the populationEventually all the individuals in the population will have the same traits

Genetic DriftGenetic Drift is most common in small populationsIn large populations there is a higher chance that individuals will find a mateGenetic Drift leads to change in relative frequency and therefor evolution

SpeciationDiversity of LifeSpeciationFormation of new speciesSpecies: organisms that breed with one another and produce fertile offspring (share the same gene pool)

Caused by natural selection and chance events

HorseMuleDonkey

How does speciation happenShared gene poolGenetic Change in 1 individual Change spreads through the population through reproduction Division/Isolation amongst the populationPopulation begins evolving independently

Reproductive IsolationDivision amongst the populationPopulation must become reproductively isolated for 2 new species to develop Allows for mutations/ changes in the gene pool to happen independently

3 types of isolation mechanismsBehavioral IsolationGeographic IsolationTemporal Isolation

Behavioral IsolationDifferent behaviors stop the individuals from being attracted to one anotherDifferent mating ritualsSongDanceColor patternAntler size

Geographic IsolationPopulation becomes separated by a geographic barrier RiverMountainBodies of waterForests The individuals cannot pass onto the other side of the barrier and therefore cannot mate

Founder EffectA small group from a population branches off and forms a NEW populationGeographically isolated from the origninal

Individuals carry alleles in different relative frequencies then the original population

Human Influence on Geographic isolation

Man made structures create geographic isolationRoadsTownsRiver Dams

Temporal IsolationReproductions times differOrganisms reproduce at specific times of the day or year Plants (morning vs. night)Animals (spring vs. summer vs. fall vs. winter)

Patterns of Evolution 17-4MicroevolutionSmall changes in a species that build over timeAccounts for closely related species

Macroevolution Large-scale evolutionary patterns and process that occur over long periods of time

Supports the idea of Common Decent Punctuated EquilibriumPatterns of long, stable periods interrupted by brief periods of more rapid change100,0001,000,000 yearsChanges come in spurtsCaused byGeographic isolationMigrationMass extinctions

Gradualism Small variations that are hard to notice over a short period of time

Variation takes place slowly (gradually)

Gradualism vs.Punctuated Equilibrium

ExtinctionThe end of a species or group of species Natural selection causes extinctionMost common cause for extinction:Species compete for limited resourcesEnvironments change individuals cant surviveWhy is extinction necessary for evolution to continue?video

Mass extinctionMass extinction: many types of living things became extinct at the same timeA the end of the Paleozoic era many organisms died out95% of the complex life in the oceans disappearedNot all organisms disappearedReason for mass extinctionCollapsing environmentCaused by multiple factors

How did the extinction of the dinosaurs allow for the diversification of mammals?

Adaptive Radiation A single species evolves into diverse forms that live in different ways

Convergent Evolution Process in which unrelated organisms come to resemble each other (Analogous Structures)side effect of adaptive radiationTakes place among different species that live in similar ecological environments Face similar environmental demands

Coevolution The process where 2 species evolve in response to changes in each otherEvolutionary change in one organism induces change in the otherFlowers/pollinatorPredator/Prey

Genetic EquilibriumHardy-Weinberg PrinciplePopulation GeneticsEvolution is the change in frequencies of alleles in the gene pool of a population

The gene pool has been shifted toward the b allele

Parent GenerationF1 offspring Allele- B92%82%Allele- b8%18%

Genetic EquilibriumGenetic EquilibriumThe situation in which allele frequencies stay the same with each new generationParent GenerationF1 offspring Allele- B92%92%Allele- b8%8%How likely is it that the allele frequencies will stay the same from one generation to the next?

Hardy-Weinberg principleAllele frequencies in a population will stay constant unless one or more of the factors are violated

What are some conditions under which NO evolution will occur?

Maintaining equilibrium Genetic Equilibrium:Random matingLarge populationNo movement into or outNo mutationsNo natural selection

Each of these things can cause evolution to take place!

Random MatingAll individuals must have an equal opportunity to reproduce

In nature is mating completely random? Why or why not?Large populationsLarge populations decrease the chances of genetic drift taking place

Why is genetic drift not as common in large populations?

No movement into or outWhen individuals move into a population or out of it, the gene pool will change

No mutationsWhat role do mutations play in evolution?Mutations introduce new alleles into the population

No natural selection Natural selection gives one phenotype the advantage over the other

Real Life?Does the Hardy-Weinberg equilibrium exist in real life? Random matingLarge populationNo movement into or outNo mutationsNo natural selection

Evolution is inevitable In most populations evolution happens!