ECOL 182R 1st Edition Lecture 1 Outline of Last Lecture I Aristotle a Great Chain of Being II Carolus Linnaeus a Binomial nomenclature phylogenetic trees III Charles Darwin a Natural selection and its requirements b Forms of natural selection Outline of Current Lecture I Alleles a Frequencies over time II Four mechanisms of evolution a Natural selection b Genetic drif c Gene flow d Mutation Current Lecture Evolution a change in allele frequency over time in a population of organisms Population a group of potentially interbreeding individuals of the same species usually in same geographic area a All catfish of same species in a given lake b All E Coli bacteria in your stomach Allele form of a gene Allele frequency proportion of that allele in a particular population Example blood type The Gene Pool Diploid Individuals have 2 copies of gene X Genotypes for gene X Allele frequencies over time Increases decreases increases returns to original point Evolution No change in line No evolution Steady upward Evolution Because evolution occurs when allele frequencies change Four mechanisms of evolution Natural Selection Individuals in a population need to vary in some trait At least some variation is genetically based Certain genotypes produce more surviving offspring than others Difference in reproduction due to agent of selection Pepper moth industrial revolution killed lichens and put black soot on instead A dark morph appeared that matched sooty surface Since then dark and light morphs have different alleles at a single gene Agent of selection is insectivorous bird Then the air quality improved so frequency of dark morph declined rapidly afer the sulfur dioxide pollution was reduced and lichens returned Those moths follow the natural selection requirements because they vary in color pattern 1 dark and light morphs are encoded by different alleles 2 the diff types survived better at diff times 3 and birds are the agent of selection 4 c Humans can be agents of natural selection such as resistance to antibiotics Bacteria are evolving and encountering antibiotics but not all of them Resulting in some bacteria developing resistance mechanisms We should reduce antibiotics in meat production that they are prescribed for the correct reasons etc Tuberculosis TB is a disease of the lungs and other tissues caused by bacterium Vaccine and antibiotics because sharp decline in cases by 1950 Patient diagnosed treated looked healthy in x rays then died Doctors found in autopsy that a genome of resistant strain difference in one DNA base pair in a protein involved in resistance Resulted in 1 amino acid difference HIV resistance to drugs is a concern Right now 8 million people on anti retroviral drugs as many as 24 million untreated Public health officials are encouraging new medicine that might cause another AIDS epidemic Big horned sheep becoming smaller Why Hunters very interested in shooting ones with largest horns We are the agent of selection Fishing Gill nets catch fish of a particular size Large sized nets select for fish that grow more slowly and are smaller as adults SO Industrial melanism in peppered moths resistance to antibiotics in bacteria evolution of virulence in viruses resistance to herbicides by weedy plants resistance to pesticides by insects reduction in fish size due to nets all involve genetic changes in populations Genetic Drif Is due to random changes in allele frequency from one generation to the next There is NO agent of selection Change in frequency due to chance Can lead to loss of alleles and fixation of others Fixation frequency is 100 Small populations are more susceptible to loss and fixation of alleles because role of chance is greater Better chance of losing populations Genetic drif in Galapagos Turtles on Alcedo Volcano Population is 4000 individuals DNA fingerprinting shows that more than 90 of then descended from ONE female They hypothesized that low genetic variability due to severe population bottleneck a way to get genetic drif It s like shaking beans from a jar probably because by volcanic eruption Cheetahs and prairie chicken populations also experiences population bottlenecks Both species are endangered Losing genetic variation d Reduced genetic variation threaten populations because they can t adapt when environment changes Population may go extinct Cancause significant evolutionary change but does NOT make organisms adapted to their environment Just one process does that which is natural selection Gene Flow The transfer of alleles from one population to another that usually involves movement of individuals White goose flies to flock of brown geese Which is evolution because it is a change in allele frequency within a population Can counter local effects of natural selection For example a second lizard species has white morph in the white sand dunes and brown genotypes disperse frequently from scrub into white dunes and breed together Mutation Alteration of a gene that gives rise to a new allele that usually involves change in DNA sequence point mutation is ONE nucleotide change Some Drosophila fruit fly behavior mutants generate in a lab using radiation or chemical mutagens They re rare per gene but common per genome Rarely generate entirely new traits they usually change pre existing traits which is usually deleterious or harmful Ultimately mutations in germ cells are the source of almost all genetic variation in a population Germ cells reproductive cells which go on to form the next generation In other words without mutation evolution would eventually stop In the White Sand Dunes there are THREE species of lizards with white morphs In each species white morph is caused by a loss of function mutation in a gene coding for melacortin 1 receptor protein In each species the mutation is different They are in THREE different positions in the DNA What two evolutionary processes are responsible for increase in white lizards in sand dunes Natural Selection and Mutation What kind of variation in a trait is required for evolution to occur Genetically based variation What kind of variation will NOT result in evolution Environmentally based