Evolution of Populations (Ch. 23)

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Evolution of Populations (Ch. 23). Doonesbury - Sunday February 8, 2004. One species, two populations. MAP AREA. CANADA. ALASKA. Beaufort Sea. Porcupine herd range. NORTHWEST TERRITORIES. Fairbanks. Fortymile herd range. Whitehorse. ALASKA YUKON. Populations evolve. - PowerPoint PPT Presentation


2.4 measuring evolution of populations2010edit

Evolution of Populations(Ch. 23)Doonesbury - Sunday February 8, 2004


One species, two populationsMAPAREAALASKACANADABeaufort SeaPorcupineherd range Fairbanks WhitehorseFortymileherd rangeNORTHWESTTERRITORIESALASKAYUKON

Populations evolveNatural selection acts on individualsdifferential survivaldifferential reproductive successPopulations evolvegenetic makeup of population changes over time favorable traits (greater fitness) become more common

Presence of lactate dehydrogenaseMummichog3The Mummichog (Fundulus heteroclitus heteroclitus) is a small killifish found in the eastern United States. It is capable of tolerating highly variable salinity and temperatures, and is found in estuaries and saltmarshes as well as less salty waters. A year-round resident of tidal creeks and wetlands, this brownish-green saltwater minnow may reach a maximum length of 5 inches. Its Indian name means "they go in great numbers." It is also known as the common killifish.A hardy fish, the mummichog is an important food source for larger fish and is often used as bait. The mummichog also has been used as a natural method of mosquito control in marsh ponds and ditches. It has been reported that one mummichog can eat as many as 2,000 mosquito larvae ("wrigglers") a day. The mummichog also feeds on other insects, small fish, crustaceans, and plant material. Because of the extreme hardiness of the species, it is sometimes the only species found in severely polluted and oxygen-deprived streams, such as the Hackensack River and the Arthur Kill in New Jersey during the height of the water pollution problem in the United States. In 1973 the Mummichog became the first fish in space when carried on Skylab 3 as part of the biological experiments package later space missions by the U.S., such as Bion 3, have also carried Mummichog.

Changes in populations

Bent Grass on toxic mine sitePocket Mice in desert lava flows

PesticidemoleculeInsect cellmembraneTarget siteResistanttarget siteInsecticide resistance

Target siteDecreased number of target sites

4Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field

2007-2008Individuals DONT evolveIndividuals survive or dont survive

Populations evolve

Individuals reproduce or dontIndividuals are selectedPopulations evolve!5FitnessSurvival & Reproductive successindividuals with one phenotype leave more surviving offspring

Body size & egg laying in water striders6Variation & natural selection Variation is the raw material for natural selectionthere have to be differences within populationsome individuals must be more fit than others


Mean beak depth of parents (mm)Medium ground finch8891011910111977198019821984Dry yearDry yearDry yearWet yearBeak depthBeak depth ofoffspring (mm)Where does Variation come from?

Mutationrandom changes to DNAerrors in gamete productionenvironmental damageSex mixing of allelesrecombination of allelesnew arrangements in every offspring new combinations of traitsspreads variationoffspring inherit traits from parent85 Agents of evolutionary changeMutation

Gene Flow

Genetic Drift

SelectionNon-random mating

91. Mutation & Variation Mutation creates variationnew mutations are constantly appearingMutation changes DNA sequencechanges amino acid sequence?changes protein?changes structure?changes function?changes in protein may change phenotype & therefore change fitness

10Every individual has hundreds of mutations

1 in 100,000 bases copied3 billion bases in human genomeBut most happen in introns, spacers, junk of various kindNot every mutation has a visible effect.

Some effects on subtle.May just affect rate of expression of a gene.2. Gene FlowMovement of individuals & alleles in & out of populationsseed & pollen distribution by wind & insectmigration of animalscauses genetic mixing across regionsreduce differences between populations

11Human evolution todayGene flow in human populations is increasing todaytransferring alleles between populations

Are we moving towards a blended world?123. Non-random matingSexual selection


WarblerfinchTree finchesGround finches4. Genetic driftEffect of chance eventsfounder effectBottleneck

141 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families

Genghis Khan tracked through Y chromosome.

Conservation issuesBottlenecking is an important concept in conservation biology of endangered speciesloss of alleles from gene poolreduces variationreduces adaptability

Breeding programs must consciously outcrossPeregrine FalconGolden Lion Tamarin155. Natural selectionDifferential survival & reproduction due to changing environmental conditions climate changefood source availabilitypredators, parasites, diseasestoxinscombinations of alleles that provide fitness increase in the populationadaptive evolutionary change


Any Questions??172007-2008

MeasuringEvolution of Populations(aka Enter Math)Ch. 23185 Agents of evolutionary change

MutationGene FlowGenetic DriftSelectionNon-random mating19Brief Terminology ReviewGene determines a trait (ex. eye color)Allele A variant of a gene (ex. brown eyes vs. blue eyes)All sexually reproducing organisms have 2 alleles for any trait.Dominant An allele that will show a trait, regardless of the other other allele (ex. brown eyes)Recessive An allele that will only show a trait if both alleles are recessive (ex. blue eyes) New TerminologyHomozygous any individual who has 2 copies of the same allele. Can be homozygous dominant or homozygous recessive.

Heterozygous- any individual who has one copy of a dominant allele and one copy of a recessive allele. WILL SHOW THE DOMINANT TRAIT!

Populations & gene poolsConceptsa population is a localized group of interbreeding individualsgene pool is collection of alleles in the populationremember difference between alleles & genes!allele frequency is how common is that allele in the population how many A vs. a in whole population22Evolution of populationsEvolution = change in allele frequencies in a populationhypothetical: what conditions would cause allele frequencies to not change?non-evolving populationREMOVE all agents of evolutionary changevery large population size (no genetic drift)no migration (no gene flow in or out)no mutation (no genetic change)random mating (no sexual selection)no natural selection (everyone is equally fit)23Hardy-Weinberg equilibriumHypothetical, non-evolving populationpreserves allele frequenciesServes as a model (null hypothesis)natural populations rarely in H-W equilibriumuseful model to measure if forces are acting on a population

W. WeinbergphysicianG.H. Hardymathematician24G.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in 1908. Their formula predicts the expected genotype frequencies using the allele frequencies in a diploid Mendelian population. They were concerned with questions like "what happens to the frequencies of alleles in a population over time?" and "would you expect to see alleles disappear or become more frequent over time?"Hardy-Weinberg theoremCounting Allelesassume 2 alleles = B, bfrequency of dominant allele (B) = p frequency of recessive allele (b) = q frequencies must add to 1 (100%), so: p + q = 1

bbBbBB25Hardy-Weinberg theoremCounting Individualsfrequency of homozygous dominant: p x p = p2 frequency of homozygous recessive: q x q = q2 frequency of heterozygotes: (p x q) + (q x p) = 2pqfrequencies of all individuals must add to 1 (100%), so: p2 + 2pq + q2 = 1

bbBbBB26H-W formulasAlleles:p + q = 1

Individuals:p2 + 2pq + q2 = 1


What are the genotype frequencies?Using Hardy-Weinberg equationq2 (bb): 16/100 = .16q (b): .16 = 0.4p (B): 1 - 0.4 = 0.6population: 100 cats84 black, 16 whiteHow many of each genotype?bbBbBBp2=.362pq=.48q2=.16Must assume population is in H-W equilibrium!28Using Hardy-Weinberg equation

bbBbBBp2=.362pq=.48q2=.16Assuming H-W equilibriumSampled data

bbBbBBp2=.742pq=.10q2=.16How do you explain the data? p2=.202pq=.64q2=.16How do you explain the data? Null hypothesis 29Sampled data 1:Hybrids are in some way weaker.Immigration in from an external population that is predomiantly homozygous BNon-random mating... white cats tend to mate with white cats and black cats tend to mate with black cats.

Sampled data 2:Heterozygote advantage.

Whats preventing this population from being in equilibrium.Application of H-W principleSickle cell anemiainherit a mutation in gene coding for hemoglobinoxygen-carrying blood proteinrecessive allele = HsHsnormal allele = Hblow oxygen levels causes RBC to sicklebreakdown of RBCclogging small blood vesselsdamage to organsoften lethal


Sickle cell frequencyHigh frequency of heterozygotes 1 in 5 in Central Africans = HbHsunusual for allele with severe detrimental effects in homozygotes1 in 100 = HsHsusually die before reproductive ageWhy is the Hs allele maintained at such high levels in African populations?Suggests some selective advantage of being heterozygous31Sickle Cell:In tropical Africa, where malaria is common, the sickle-cell allele is both an advantage & disadvantage. Reduces infection by malaria parasite.

Cystic fibrosis: Cystic fibrosis carriers are thought to be more resistant to cholera: 1:25, or 4% of Caucasians are carriers Cc


Single-celled eukaryote parasite (Plasmo