Presentation on theme: "Lamarck vs Darwin worksheet Bell Ringer"— Presentation transcript:
1 Lamarck vs Darwin worksheet Bell Ringer Agenda:Early Morning LabLamarck vs Darwin worksheetBell RingerNotes over Genetic Drift and Hardy WeinbergHardy Weinberg/Genetic Drift worksheetObjective:I can explain genetic drift and calculate allele frequency using Hardy-Weinberg.
2 In addition to natural selection, evolutionary change is also driven by random processes…
3 II. GENETIC DRIFTThe smaller the population, the less genetic variety it has.In a very small population, alleles can be lost from one generation to the next, simply by random chance.When a population evolves only because of this type of random sampling error, GENETIC DRIFT is taking place.
4 Genetic DriftChance events changing frequency of traits in a populationnot adaptation to environmental conditionsnot selectionfounder effectsmall group splinters off & starts a new colonyit’s random who joins the groupbottlenecka disaster reduces population to small number & then population recovers & expands again but from a limited gene poolwho survives disaster may be randomFounders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonistsexample: colonization of New WorldBottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance eventalleles lost from gene pool not due to fitness, narrows the gene pool
7 Ex: Cheetahs All cheetahs share a small number of alleles less than 1% diversity2 bottlenecks10,000 years agoIce Agelast 100 yearspoaching & loss of habitat
8 Conservation issuesPeregrine FalconBottlenecking is an important concept in conservation biology of endangered speciesloss of alleles from gene poolreduces variationreduces adaptabilityBreeding programs must consciously outcrossGolden Lion Tamarin
9 Human Impact on variation How do we affect variation in other populations?Artificial selection/InbreedingAnimal breedsLoss of genetic diversityInsecticide usageOveruse of antibioticsresistant bacterial strains
10 Hardy Weinberg: Population Genetics Using mathematical approaches to calculate changes in allele frequencies…this is evidence of evolution.
11 Hardy-Weinberg equilibrium Hypothetical, non-evolving populationpreserves allele frequenciesnatural populations rarely in H-W equilibriumuseful model to measure if forces are acting on a populationmeasuring evolutionary changeG.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in 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?"G.H. HardymathematicianW. Weinbergphysician
12 Evolution of populations Evolution = change in allele frequencies in a populationhypothetical: what conditions would cause allele frequencies to not change?very 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)H-W occurs ONLY in non-evolving populations!
13 Populations & gene pools Conceptsa 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 populationhow many A vs. a in whole population
14 H-W formulas Alleles: p + q = 1 Individuals: p2 + 2pq + q2 = 1 B b BB
15 Origin of the Equation p2 + 2pq + q2 Assuming that a trait is recessive or dominantAllele pairs AA, Aa, aa would exist in a populationp + q = 1The probability that an individual would contribute an A is called pThe probability that an individual would contribute an a is called qBecause only A and a are present in the population the probability that an individual would donate one or the other is 100%p2 + 2pq + q2Male Gametes A(p)Male Gametes a(q)Female gametes A(p)AAp2AapqFemale Gametes a(q)aaq2
16 Hardy-Weinberg theorem Frequencies are usually written as decimals!Counting Allelesassume 2 alleles = B, bfrequency of dominant allele (B) = pfrequency of recessive allele (b) = qfrequencies must add to 1 (100%), so:p + q = 1BBBbbb
17 Hardy-Weinberg theorem Counting Individualsfrequency of homozygous dominant: p x p = p2frequency of homozygous recessive: q x q = q2frequency of heterozygotes: (p x q) + (q x p) = 2pqfrequencies of all individuals must add to 1 (100%), so:p2 + 2pq + q2 = 1BBBbbb
18 Practice Problem:In a population of 100 cats, there are 16 white ones. White fur is recessive to black.What are the frequencies of the genotypes?
19 Use Hardy-Weinberg equation! q2 (bb): 16/100 = .16q (b): √.16 = 0.4p (B): = 0.6p2=.362pq=.48q2=.16BBBbbbMust assume population is in H-W equilibrium!What are the genotype frequencies?
20 Answers: Assuming H-W equilibrium: Expected data Observed data 2pq=.48q2=.16Assuming H-W equilibrium:Expected dataBBBbbbp2=.20p2=.742pq=.102pq=.64q2=.16q2=.16Sampled 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.What’s preventing this population from being in equilibrium.bbBbBBObserved dataHow do you explain the data?How do you explain the data?
21 Tips for Solving HW Problems: Solve for q first.Then solve for p.Don’t assume you can just solve for p2 if only given dominant phenotypic frequency.READ carefully!!!