Outline of Last LectureOutline of Current LectureMechanisms of Evolutionary ChangeNatural SelectionImportanceBe sure you understand that ….Evolution – Pattern and ProcessMechanisms of Evolutionary Change – Part 2How do you test for evolution?What does the excess of heterozygotes mean?MutationMisconceptions about MutationsMigrationGenetic DriftReviewBIO SCI 150 1st Edition Lecture 14Outline of Last Lecture 1. Evolution a. Key termsb. Evolutioni. Pattern and Processii. Misconceptionsc. Scientific Explanationsd. Evolution as a theoryi. Pattern of EvolutionOutline of Current Lecture 1. Mechanisms of Evolutionary Changea. Natural Selectioni. Importanceii. Processb. How to test for evolutionc. Mutationsi. Misconceptionsd. Migratione. Genetic DrifMechanisms of Evolutionary Change- Natural selection- Mutation- Migration (= gene flow)- Genetic drif - bottlenecks and founder eventsNatural Selection How does Natural Selection work? see p. 302-305Natural selection occurs when three conditions are met: 1. Individuals within a population vary in their characteristics (traits).2. The variable traits are heritable.3. These traits help individuals survive better or reproduce more- Example: Galapagos finches, wild mustardThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Artificial selection = Natural selection (just caused by man)- “If animal breeders could produce these different varieties in a few generations, think what could be accomplished in hundreds or thousands of generations”o Charles Darwin, On the Origin of Species – 1859Importance- Explains how organisms adapt to changing environmentso Adaptation: inherited characteristics that increase survival or reproductiono Fitness: reproductive success (# offspring)- Provides a mechanism for Evolutiono Nat. Selection: differential survival and reproduction of genotypesBe sure you understand that …. 1. Individuals do not adapt, only populationsa. Natural selection acts on individuals, but evolutionary change occurs in populations. i. i.e., only populations evolve2. Evolution has no goals (it is not “progressive”)a. Natural selection does not grant organisms what they “need”3. But …Natural Selection is not randoma. It creates organisms that are better able to survive or reproduce – under existing conditions4. Animals do not act for the “good of the species”a. i.e., Disney Movie: Lemmings commit mass suicide when populations become largei. If a "self-sacrifice" gene existed, it would quickly be out-competed by "cheater" genesEvolution – Pattern and ProcessEvolution is “descent with modification” - Both a Patterno Organisms are related by descent from common ancestorso Organisms have changed over time- And a Processo Natural Selection Individuals within a population vary in their characteristics (traits). The variable traits are heritable. These traits help individuals survive better or reproduce moreMechanisms of Evolutionary Change – Part 2Mechanisms that change allele frequencies in populations: - Natural selection- Mutation- Migration (= gene flow)- Genetic drif (= nonrandom sampling of small populations)Natural selection is the only mechanism that results in adaptation and leads to increased fitness…but natural selection is just one of four mechanisms that can cause EvolutionEvolutionary Processes (Ch 24)Modern definition of Evolution: a change in allele (gene) frequencies over time. - Alleles - Alternate forms of a gene- Allele Freq. = Proportion of R (or r) alleles in the populationHow do you test for evolution?Examine Allele Frequency Change with The Hardy-Weinberg Model- The model predicts the allele and genotype frequencies when there is no evolution, that is:o no natural selection (random mating)o no mutation o no migration (isolated)o no genetic drif (large population)- AKA Punnett squareWhen in H-W equilibrium...1) Allele frequencies stay the same (0.7, 0.3)a. Like shuffling a deck of cards; the number of different cards remains the same2) Genotype frequencies are given by:b. Assumes random mating and no change in Allele frequenciesFound more heterozygotes and fewer homozygotes than expected under H-W What does the excess of heterozygotes mean?Not due to mutation, migration or drifTwo possibilities1) Non-random mating with respect to MHC - Women prefer males with dissimilar MHC genotypes2) Heterozygote advantage at MHC - Couples with dissimilar MHC genotypes are more likely to produce kidsMutation- Mutation is the ultimate source of genetic variability. Mutations occur randomly during DNA replication and meiosis.- Mutations are rare (1 every 1000 offspring) at any particular gene, but humans have ~25,000 genes. - We all have mutations!o 175 per personMisconceptions about Mutations1) All mutations are bad a. No, many are "silent" (p. 313)i. (synonymous changes in codons)ii. Redundancy of genetic code2) Random mutations cannot account for the adaptations of living organismsa. Mutation in MC1R gene causes melanismi. 40 "mutants" in 1 billion miceHow rare are beneficial mutations? 1/75 million…but Random mutations combined with Natural Selection can account for the adaptations of living organismsThe probability that the mutation will spread depends on: 1) intensity of selection and 2) population sizeMigrationMigration refers to the movement of alleles between populations. This is known as gene flow. Genetic Drift- This is any change in the allele frequencies in a population that is due to random chance. - Genetic drif is much more pronounced in small populations. - Small populations may result from founder or bottleneck eventso Change in allele frequency due to random chance See Fig 15.8 Ex: greater prairie-chickens- Genetic Drif leads to lower Genetic variation and reproduction- Founder event: A few individuals colonizeReview1. Evolution is measured as change in allele frequencies in a population.2. Four mechanisms change allele frequencies in populations: Mutation, Migration, Genetic drif & Natural selection3. Only Natural Selection causes adaptive evolutionary change 4. Adaptation: a. 1) traits that increase fitness, or2) the process of evolutionary