Lecture outlines – Part 1: EvolutionLecture outlines – Part 1: Evolution Evolution lecture 1 - Pre-Darwinian thoughtA - Pre-Darwinian thoughti) Natural theology (Creationism): species FIXEDii) Linnaeusiii) Catastrophism: Cuvier and the search for Mastodoniv) Gradualism and uniformitarianism: Hutton & Lyell.v) Age of the earth: Usher and Kelvinvi) Evolution at last : Lamarck: Use and disuse, Inheritance of acquired characteristicsvii) Erasmus DarwinB - Darwin’s evidence and influencesEvidence: Ricness of tropical forests, Fossils, Oceanic islands and Geographic distributionsInfluences: Lyell’s principles of Geology, Malthus ‘Essays on the principles of populations’, Artificial selection andObservations during voyage of Beagle (see above)Evolution lecture 2 - Darwin and the genetic basis of evolutionA - Darwin’s theoryWhat it said – i) Descent with modificationii) Natural selection is the mechanism of changeRemember though – i) Individuals do not evolve, populations doii) Natural selection can only amplify HERITABLE variationiii) Not all variation is heritable, much is environmentalProblems in Darwin’s dayi) ‘Blending’ theory of inheritance would dilute variabilityii) How can selection recognize such small differences?iii) Is the earth old enough? More evidence: Artificial selection, Systematics, Biogeography, Comparative anatomy, Comparative embryology, Fossils and now Molecular biologyWhat is Evolution? Make sure you understand this. When people say they don’t believe in Evolution they are probably using a different definition. Darwin presented overwhelming evidence for evolution having occurred and proposed a specific theory (natural selection) to explain the mechanism of evolution. B - Mendellian genetics – terms to remember: character, true-breeding, trait, F1, F2, homozygous, heterozygous, genotype, phenotype, monohybrid cross, dihybrid cross, testcross i) Mendel’s law of segregation (using modern terminology)Allele pairs segregate during gamete formation (meiosis), and the paired condition is restored by the random fusion of gametes at fertilization.ii) Mendel’s law of independent assortment (using modern terminology)Each allele pair segregates independently of other gene pairs during gamete formationiii) Mendelian genetics involve the application of these two simple laws and two basic laws of probability.Rule of multiplication – the probability that independent events will occur simultaneously is the product of their individual probabilities.Rule of addition – the probability that an event can occur in two or more independent ways is the sum of the separate probabilities of the different ways.Evolution lecture 3 - Population geneticsA - Beyond Mendellian geneticsi) Incomplete dominance – dominant phenotype is not fully expressed in the heterozygoteii) Codominance – full expression of both alleles in the heterozygoteiii) Multiple alleles – each individual can posses only two alleles but there may be many in the population iv) Pleiotropic (single genes may have many effects) and polygenic (character determined by many segregating loci) traits.v) Epistasis – one gene may modify the expression of anothervi) Environmental effects – gene expression may be affected by the environmentvii) Linked genes – genes on the same chromosome will not assort independentlyviii) Recombination – but recombination may sometimes separate even closely linked genesix) Sex-linked genes – genes on the X but not the Y chromosome John Latto 6/21/07B - Genetic pedigreesi) Autosomal dominant genetic disordersii) Autosomal recessive disordersiii) Recessive X-linked genetic disorders Make sure you understand the simple basics of Mendelian genetics. We can use these simple rules with the rules of probability to answer surprisingly complex questions. Try answering the questions at the end of Chapter 14 in Campbell. Every year people ask meabout question 11 (6th) or 9 (7th). It isn’t a ‘trick’ question but you do have to use ALL the information you have been givenTerminology review – make sure you know the following because we’ll be using them:Gene, Allele, Locus, Homozygous, Heterozygous, Dominant, RecessiveC - Individuals vs. populationsi) Lifespan – one generation vs. many generationsii) Genetic characteristics – genotype vs. gene pooliii) Evolutionary characteristics – no change vs. changeD - Hardy-Weinberg principlei) Gene frequencies will remain unchanged under certain conditions (an ‘ideal’ population)Large population + Isolated population + No mutations + Random mating + No natural selectionii) If p is the proportion of allele A and q is the proportion of allele a (thus p + q = 1) then after 1 generation of random mating in an ideal population the genotypes will attain and remain at the following frequencies:Genotype FrequencyAA p2Aa 2pqaa q2Evolution lecture 4 - MicroevolutionA - Significance of Hardy-Weinberg principlei) Gene frequencies DO change over time (this is known as MICROEVOLUTION)ii) Without the H-W principle we wouldn’t know:- how to detect this change- the magnitude of the change- the direction of the change- how to begin looking for a cause for the change.iii) H-W principle tells us what happens in the absence of change so we can then detect and measure that change, much as Newton’s first law of motion does for moving bodies.B - Microevolution - when Hardy-Weinberg conditions do not applyi) Genetic drift: Founder effect and genetic bottlenecks - Conservation implicationsii) Gene flow (migration)Individuals may move between populations or gametes may move (e.g. pollen)iii) MutationsMutations are the source of genetic variation – the raw material for evolutionary changeBut mutation alone does not cause significant changes in allele frequencies.iv) Non-random mating (note: non-random mating will change genotype frequencies but not allele frequencies)Inbreeding and inbreeding depression (costs seen in the lengths species go to to avoid inbreeding).Conservation implications again.Assortative matingv) Natural selection (differential reproductive success)How much variation is there in natural populations? Two theories in the 1940’s and 1950’sHow is variability maintained? Diploidy and balanced polymorphismsWhat can maintain a balanced polymorphism? - Heterozygote advantage- Frequency dependent selection- Patchy environment John Latto
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