BCOR 12 1nd Edition Lecture 6 Outline of Last Lecture I Types of Natural Selection II Biological Species Concept III Speciation IV Reproductive Barriers Outline of Current Lecture I Macro and microevolution II Reclassification of species III Allopatric speciation and sympatric speciation IV Hybrid Zone Current Lecture Macroevolution the pattern of evolution speciation Microevolution the process of evolution forces that cause allele frequencies to change in population o Both are occurring and affect on another o How do these two unify to become evolution Reclassification Reclassification of species going from two separate species to one can occur if the two species follow the definition of a species which is that they interbreed in nature and their offspring survive and reproduce o Important to note definition of species is that they interbreed in NATURE if a question asks about two species that make in captivity but not in the wild then there is a pre or post zygotic barrier between the two for their interbreeding does not follow the definition Reclassification happens when new evidence is presented on the subject to show that either one species is actually two or vice versa o New evidence is often DNA or based on very in depth observations on species Speciation There are two types of speciation These 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 o Allopatric a geographic separation between members of a species which interrupts gene flow o Sympatric speciation a biological process occurs that interrupts gene flow while members of the same species are in contact with one another SPECIATION CAN OCCUR WITH OR WITHOUT GEOGRAPHIC SEPARATION Important notes geographic separation DOES not cause speciation a different mechanism causes this Natural Selection Important notes geographic separation is NOT the biological barriers BUT it can lead to a biological barrier between members of the species which are now separated and would then causes members of the species to be unable to interbreed when if they are reunited then speciation has occurred A barrier that keeps species from interbreeding after a geographical barrier has been removed is a pre and postzygotic barrier for it minimizes gene flow Processes that cause Sympatric speciation Polyploidy a chromosomal alteration which an organism possesses more than two complete chromosome sets x diploid This process occurs during meiosis o Extremely common in plants Habitat differentiation the species has two habitats it can live in and the differences in the habitat lead to differences among the species o Ex Flies living in a tree that develop quickly have to develop quickly as well in order to take advantage of the tree s fruit while the same species of fly on a different tree that develops slowly do not have to develop and mate as quickly Sexual selection one sex of the species chooses their mate and are rather choosy and base it one physical characteristics o Ex Cichlid fish females choose their mates based on the color they think is desirable In one species this is orange while in another it is blue If species in the same geographic range cannot mix their gametes then they are sympatric species and there is a prezygotic barrier Hybrid Zones Hybrid zones where two different species overlap and mate to create hybrid offspring Studies in hybrid zones reveal factors that cause reproductive isolation Three events can take place o Reinforcement the strengthening of reproductive barriers between the two species and hybrids over time cease to form remain SEPARATE species o Fusion weakening of reproductive barriers and the two species fuse into one if hybrid offspring are viable and fertile o Stability the continued production of hybrids Here hybrids do not mate with their parent species but there is possibility that they mate with other hybrids