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Warm Up •Which undergoes evolution … • Individuals or populations? What the……. • http://msnvideo.msn.com/?channelindex=4 &from=en-us_msnhp#/video/2699c2f5dfa2-413d-9314-ff6326eea288 Chapter 16 Evolution of populations Variation and gene pools • Gene pool – consists of all genes • Genetic variation – 2 main sources • Mutation –Change in sequence of DNA • Crossing over –Occurs during production of gametes Process of speciation • As new species evolve, populations become reproductively isolated from each other by three main concepts – Behavioral isolation – Geographic isolation – Temporal isolation What is reproductive isolation? • When members of two populations cannot interbreed and produce fertile offspring…. – Reproductive isolation occurs • Now have separate gene pools • Respond to natural selection and genetic drift as different units. Behavioral Isolation – leads to reproductive isolation Very common mechanism used to keep closely related animals from interbreeding Include differences in … •courtship behavior •chemical signals •mating calls • Geographic Isolation – leads to reproductive isolation Two populations separated by geographic barrier – Rivers – Mountains – Bodies of water • Natural selection now works separately on both populations • Apert and Kaibab squirrels – Separated by Colorado river aprox. 10,000 yrs ago. Temporal Isolation – leads to reproductive isolation • 2 or more species reproduce at different times – Leads to speciation because • Unlikely to reproduce with each other • Then may become separate species Warm Up • ________________ is when two species breed at different times. Evolution of Populations Evolution of Populations Part 2 Part 2 Natural Selection on Polygenic Traits Directional Stabilizing Disruptive • Natural Selection on Polygenic Traits Directional – whole populations range shifts – Ex. Average height of humans is taller now • Stabilizing - whole populations range gets larger • Disruptive – populations range gets disrupted – Ex. If disease struck humans that only affected middle aged people. Testing natural selection in nature • Natural selection – Individuals with different traits have different chances of survival during a environmental event • Galapagos finches –When food scarce on island due to drought, finches with largest beaks most likely to survive Rapid Evolution Natural selection takes place frequently and sometimes very rapidly – Ex. Galapagos finches • Due to drought, next generation of finches had larger beaks than did generation before selection had occurred. • Finches had evolved rapidly due to natural selection Speciation in Darwin’s finches • Founders arrive – Some species foreign to area arrive • Separation in population – Some from founding group get isolated • Changes in gene pool occur – Due to separation and natural selection • Reproductive isolation – Evolved to point that neither population, if came in contact would/could reproduce • Ecological Competition – If both populations regroup in certain area, competition for similar food sources will occur • Continued Evolution – Process continues on Hardy – Weinberger formula • The Hardy-Weinberg formula allows scientists to determine whether evolution has occurred. p 2 = frequency of AA (homozygous dominant) 2pq = frequency of Aa (heterozygous) q 2 = frequency of aa (homozygous recessive) Hardy – Weinberger formula • 5 conditions are required to maintain genetic equilibrium 1. Random mating 2. Large population 3. No movement in or out of population 4.No mutations 5. No natural selection What is the chance this happens in the wild Warm Up What type of isolating mechanism is this?