How Populations Evolve Class Discussion In 17th 18th century Europe almost everyone believed in Creationism and that the earth was 6 000 years old which was worked out as an estimate by Archbishop James Ussher in 1650 I Natural Selection NS a k a Descent with modification A Observations by Darwin 1 Species tend to over reproduce 2 Individuals in a population vary B Conclusion the varied traits that an individual inherits affects this individual s ability to Secure limited resources to better survive and reproduce Traits that are better than others for a particular environment become More prevalent in the population C Natural Selection NS differential reproductive success of organisms In other words individuals whose characteristics best adapt them to their CURRENT environment are most likely to survive and reproduce Successful or fit individual an individual that is well adapted to their environment able to pass on their genes D Three key points about NS 1 NS is an editing process not a creative process What does this REALLY mean 2 NS is contingent on time and location 3 Significant evolutionary change can occur in a short time 1 II Population Genetics Charles Darwin In 1859 published theory of NS without knowing about inherited traits genes Gregor Mendel 1860 s his work was not recognized until 40 years after the Origin of Species was published Darwin therefore did not understand WHERE the variation of individuals came from Interestingly Darwin s theory was attacked because of the lack of understanding of genes it was argued that if two animals were blended like horse and zebra traits would be diluted and offspring would never have clear advantages Darwin was so unsure that he even stopped arguing his theory A Modern synthesis 1940 s The ideas of Darwin and Mendel together How is it different from Darwin s theory of NS 1 It recognizes 4 processes of evolution not just natural selection gene flow mutation genetic drift 2 It recognizes that traits inherited genes B NS acts on individuals but the effect is a change in the population C population group of organisms of the same species living at the same time place D Microevolution a change in allele frequency over time III Hardy Weinberg model of a non evolving population a k a a population that s in genetic equilibrium A Do non evolving populations exist Purely theoretical What 5 conditions would have to be met Large population no mutations can occur no immigration and emigration random mating reproductive success no natural selection Mutations Size Immigration Emmigration Mating Reproductive success B Hardy Weinberg Principle 1908 sexual reproduction alone does not cause or lead to evolution 2 Butterfly example an imaginary butterfly population is in genetic equilibrium a k a HardyWeinberg equilibrium 1 000 individuals Population 490 A A dark blue 490 49 49 420 A a medium blue 420 42 42 a a white 90 09 9 90 What are the individual genotype frequencies in the population A A 49 A a 42 a a 9 What are the allele frequencies in the population Total Alleles 2 000 A 1400 2000 70 a 600 2000 30 What will the individual genotype frequencies be in this population in the next generation if nothing other than sexual reproduction is occurring A 7 a 3 A 7 AA 49 Aa 21 a 3 Aa 21 aa 09 C HW equations to know p dominant trait q recessive trait 1 p q 1 use to find allele frequencies 2 p 2 2pq q 2 1 D Try an example problem An imaginary blue footed booby population in the Galapagos Islands is in Hardy Weinberg equilibrium The frequency of the recessive allele for webbed feet is 0 4 What is the frequency of individuals that have non webbed feet q 4 p 1 q 6 punnet square 84 for dominant trait p 2 2pq 84 non webbed 3 The Hardy Weinberg principle assumes that only sexual reproduction occurs in a population and that no other forces are at play resulting in genetic equilibrium and no evolution of a population THIS IS NOT REALITY ALL POPULATIONS ARE EVOLVING So what types of forces lead to microevolution i e changes in allele frequency Working in groups of three use the words below to compose a sentence that explains your view of co evolution You can use additional words You can duplicate words Don t need to use all the words provided Make a list of the unused words Co evolution Try Species Allele Evolution Frequency Design Evolve Response Demand Need Intend Seek Want Selective force Decide Change Adapt Sentence 4 The Origin of Species Class Discussion I Concepts of Species A Ernst Mayr s Biological Species Concept a group of populations whose individuals have the potential to interbreed B Alternative definitions are needed Why Fossils and prokaryotes We cannot know how fossils for example reproduce Prokaryotes have asexual reproduction C Reproductive Barriers why can t related species mate List some ideas 1 Five pre zygotic Barriers and examples a behavioral different courtships prevent mating b habitat species live in different places c temporal breeding occurs at different time of year or day d gemetic isolation when male and female gametes fail to unite e mechanical isolation differences in physical structures prevents successful mating 2 Three post zygotic Barriers and examples a reduced hybrid fertility hybrids fail to reproduce functional gametes b reduced hybrid viability the development or survival of hybrids is impaired c hybrid breakdown offspring of a hybrid is weak 5 II How do reproductive barriers form Form when gene flow is blocked between two or more populations Within each population natural selection mutation and genetic drift can occur A Speciation1 Two species from one ancestral species ancestor Divergence 2 A burst of divergences from a single ancestor that leads to many new species each adapted to a new habitat or using new resources ancestor Adaptive radiation B Allopatric Speciation Geographical barrier impeding gene flow C Sympatric Speciation 1 Animals new species arise within the same geographic location as the parent species rare 2 Plants can become reproductively isolated in one generation due to polyploidy Ex A 2n plant species 1 if nondisjunction of all chromosomes occurs in meiosis 2n gametes form self fertilization 4n offspring This 4n offspring is now a new species species 2 But why is the 4n offspring a new species Consider a cross between the 4n species and the 2n species 4n plant makes 2n gametes and a 2n plant makes n gametes offspring are 3n Remember the biological species concept A species is a group of populations
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