Chapter 24: The Origin of SpeciesConcept 24.1: The biological species concept emphasizes reproductive isolation- Species: Latin for “kind” or “appearance”Are these the same species? - No, All eagles, not all same speciesAre these the same species? - Yes, All dogs, different kindsThe Biological Species Concept:- Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring- Cannot be applied too Asexual organismso Fossilso Organisms about which little is known regarding their reproduction Limitations of the BSCSpeciation- Dependent on:o Reproductive isolationo Genetic divergenceReproductive Isolation:- The existence of biological factors that impede members of two species from producing viable, fertile offspring- Pre-zygotic barriers- Post-zygotic barriers Pre-zygotic Barriers:- Impede mating between species or hinder the fertilization of ova if members of different species attempt to matePost-zygotic Barriers:- Often prevents the hybrid zygote from developing into a viable, fertile adult o Example: Mule is sterile Two species of pine are found in the same habitat, but release pollen at different times during the year. This is an example of ______ isolation.- Geographical- Ecological- Temporal - BehavioralIs gametic isolation a pre-zygotic or post-zygotic isolating mechanism?1. Pre-zygotic2. Post-zygotic3. It depends on the species, or whether it acts pre- or post-zygotically4. It can be either, depending on the time of year Concept 24.2: Speciation can takeplace with or without geographicseparation- Speciation can occur in twowayso Allopatric speciationo Sympatric speciationWhich of the following is notconsidered a requirement forspeciation to occur?- Populations must be isolated(geographically or in some other manner) from one another - Isolated populations must become genetically distinct from one another- Exchanges of genetic information must be restricted between populations- High levels of gene flow among populations must occur Allopatric Speciation:- “Other Country”- Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations EstablishingReproductive IsolationSympatric (“Same Country”) Speciation:- Speciation that takes place in geographically overlapping populationsPolyploidy:- Presence of extra sets of chromosomes in cells due to accidents during meiosis- Has caused sympatric speciation in many plant species- Autopolyploidy: individual has more than two chromosomes sets, all derived from a single species- Allopolyploidy: species with multiple sets of chromosomes derived from different speciesAllopolyploidyPlant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The likely diploid number for species C would be _____.a. 12b. 14c. 16d. 28, use add method to add diploid numbers from both speciese. 56Sympatric Speciation in Progress: The Apple Maggot Fly/Hawthorn FliesIn cichlid fish- Sympatric speciation has resulted from nonrandom mating due to sexual selection Example of Stability in HybridsWhich of the following is the first step in the process of allopatric speciation?a. Genetic Driftb. Interspecies contactc. Geographic isolation, “Other Country”d. Reproductive isolation All but which of the following are likely to promote sympatric speciation?a. Gene Flow, will inhibit speciation, will not produce new speciesb. Ecological isolationc. Temporal isolationd. PolyploidyConcept 24.3: Hybrid Zones Provide Opportunities to Study Factors that Cause Reproductive IsolationPossible Outcomes for HybridsThe Breakdown of Reproductive Barriers: FusionChapter 25: The History of Life on EarthEarly Earth:- The Earth is about 4.6 billion years old o Radiometric dating of meteorites & moon rocks- Life arose about 3.8 billion years agoo Chemical traces in rock 3.8 BYAo Fossil bacteria in rocks 3.5 BYA- No spontaneous generation now, but must have happened then Conditions on Early Earth:- Atmosphereo CO2, CH4, NH3, H2S, H2Oo No free oxygen- Abundant Energy to drive reactiono Frequent storms with much lighteningo Frequent volcanic eruptionso Frequent meteor impacts o Ultraviolet light from the sun Testable hypotheses explaining the origin of life:1. Abiotic synthesis of small organic molecules2. Joining these molecules into polymers3. Packaging these molecules into “protobionts”4. The origin of self-replicating molecules Miller and Urey Experiments - Electric spark simulates lightening- Gases of primeval atmosphere- Organic molecules appear after only a few days - Purpose: To determine that you can form basic organicmaterial without oxygen (Early Earth elements)Alternative Hypotheses:1. First organic compounds may have been synthesizednear hydrothermal vents2. Extraterrestrial origin – meteorites, ice, spaceAbiotic Synthesis of Polymers:- Small organic molecules polymerize when they are concentrated on hot sand or clay Protobionts:- Aggregates of abiotically produced molecules surrounded by a membrane- Liposomes can form when lipids or other organic molecules are added to waterOxygen has a _____ influence on the formation of complex organic molecules because _______.1. Positive, it increases metabolism2. Positive; it acts as a coenzyme3. Negative; it prevents photosynthesis4. Negative; it is highly reactiveThe Chicken or the Egg:Now- DNA RNA Protein- Need proteins to synthesize more DNAThen- Earliest cells used RNA to store info- Ribozymes to catalyze reactions Sequence of events first prokaryotes Which of the following statements does not support the hypothesis of an RNA world?- Single stranded RNA can assume many 3D shapes specified by their nucleotide sequence- Some RNAs are important catalysts in modern cells- The oldest known fossils contain traces of RNA- RNA can store genetic informationConcept 25.2: The fossil record documents the history of life Fossils document the history of life:- Sedimentary strata reveal the relative ages of fossilso Fossils near surface more recento Deeper fossils more ancient- Fossils records shows great changes in organismsthrough time Dating of Fossils:- Order of fossils in rock strata tells us the sequence inwhich they were laid down- This provides relative ages, not absolute datesRadiometric Dating:- Can determine absolute ages of fossilso Radioactive isotopes decay into a daughter
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