2/12/2014 1 Course Business • Lecture schedule – 1 week behind syllabus • Midterm Exam #1 – Feb. 25 1 Goals for today • Finish forces and mechanisms of evolution • Classification, Phylogeny, and Speciation 2 What is evolution? • Change in allele frequencies in a population over time • Natural selection is not the only mechanism! • Four forces or mechanisms of evolution 32/12/2014 2 Random mechanisms of evolution • Mutation • Gene flow (Migration) • Genetic drift 4 Mutation • Any alteration in the genetic material – Different levels of mutation • Somatic cells vs gametes • Single base (aka point mutation) or frameshift 5 Mutation • Why is mutation so important? – Increases variation within and among populations – Only source of novel alleles 62/12/2014 3 Gene flow (migration) • Movement of genetic material from one population to another – How will gene flow affect variability? 7 Gene flow – increase or decrease variability? 8 92/12/2014 4 Gene flow (migration) • Increases variation within a population, but decreases variation among populations 10 Genetic Drift • Changes in allele frequencies due to chance • Will this have it’s greatest effect on large or small populations? • How will genetic drift affect variation? 11 Genetic Drift • Greatest effect on small populations 122/12/2014 5 Genetic drift – increase or decrease variability? 13 14 TIME: 1 15 TIME: 22/12/2014 6 16 TIME: 3 17 TIME: 4 Genetic Drift • Reduces variation within populations but increases variation between populations 182/12/2014 7 Genetic Drift – Founder Effect • Difference in allele frequencies in a founding population compared to the allele frequencies in the source population – Ellis-Van Creveld syndrome Amish 19 Genetic Drift – Founder Effect 20 Genetic Drift – Population Bottlenecks • Relatively low level of genetic diversity – Population drastically reduced 10,000 – 12,000 years ago 212/12/2014 8 Random mechanisms of evolution • Random changes in allele frequencies do not produce adaptations 22 Any Questions? 23 Non-random mechanisms of evolution Natural Selection Sexual selection 242/12/2014 9 Natural Selection (and sexual selection) – increase or decrease variability? • Decreases variation within a population • Can increase or decrease variation between populations depending on the selection pressures. – Why is this? 25 Natural Selection • Non-random! • Three necessary and sufficient conditions: 1. [Phenotypic] variation in a trait. 2. Heritability of the trait. 3. Differential reproductive success based on that variation. • Natural selection produces adaptations! 26 Adaptations – what evidence do we have? • Complexity, design features – E.g., wings • Apparent purpose of design – Reverse engineering • Directional change through time 27 Caudipteryx zoui2/12/2014 10 Adaptations – what evidence do we have? • Convergence (homoplasy) in design – E.g., wings of insects, pterosaurs, birds, bats 28 Adaptations – what evidence do we have? • Varies in a sensible way across biological space • Has a COST – Flightless birds on isolated islands – Expensive muscles to power wings – Use it or lose it 29 Adaptations – how do they occur? • Adaptations result from the accumulations of small changes over many generations. • Each of these small changes must be beneficial for it to be a target for natural selection! 302/12/2014 11 What good is half an eye? • Half an eye is actually pretty good compared to a quarter of an eye! • Even a millionth of an eye is better than no eye at all. 31 Primitive eyes 32 http://en.wikipedia.org/wiki/File:Euglena_diagram.jpg Light Sensitivity • On a molecular level, light is powerful • Many cells are light sensitive to some degree • Many organisms, including plants, move in response to light 33 http://ww w.redrockrvpark.com/blog/uploaded_images/SunflowerLittleBack_093825-751915.jpg2/12/2014 12 Primitive Eyes 34 http://universe-review.ca/I10-82-planarian.jpg Planaria sp. Evolution of the eye in Mollusks 35 http://bcrc.bi o.umass.edu/courses/fall2010/plsoilin/plsoilin190e/review/20101123/20101123.html Adaptations – last thoughts… • Adaptation results from competition among individuals, and not between populations or groups or species 362/12/2014 13 Any Questions? 37 Four “Forces” of Evolution • Natural Selection: reduces variability within populations; its effect on variation among populations depends on the nature and pervasiveness of the selective pressure • Mutation: increases variation within and among populations • Gene Flow: increases variation within populations; reduces variation among populations • Genetic Drift: reduces variation within populations; increase variation among populations 38 Are these really forces? • Natural selection is a result of being variable, biological organisms. 392/12/2014 14 Are these really forces? • Genetic drift is a result of chance and sampling error in gamete production 40 Are these really forces? • Gene flow is a result of population movements or environmental pressures on population sizes or social structure within a population 41 Are these really forces? • Mutation is a result of error during DNA replication 422/12/2014 15 Are these really forces? • They are not magical or theoretical concepts • Evolution is simply a consequence of organisms being alive • But over time, evolution has tremendous impact on the natural world 43 Summary • Mendelian genetics – Dominant/recessive; phenotype/genotype; heterzygous/homozygous • Modern synthesis explains… – … why phenotypes appear “blended” – …how variation is maintained – …how not previously visible phenotypes are produced 44 Summary • Genetics – DNA, RNA, Proteins – Two functions of DNA – Mitosis/meiosis; gametes/somatic cells; haploid/diploid • Forces of evolution – How do they affect populations? – Random/non-random 452/12/2014 16 Classification, Phylogeny, and Speciation [part 1] 46 Objectives • How to define a species • How species form • How to classify and arrange species 47 What is a species?? 482/12/2014 17 Biological Species Concept • John Ray (1628 – 1705) • “Species are groups of reproducing organisms” • If A and B can produce [viable] offspring, then they are considered the same species. 49 Problems with the BSC? 50 Are these the same species? 512/12/2014 18 Are
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