Chapter 24 The Origin of Species Concept 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 species Are these the same species Yes All dogs different kinds The 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 to o Asexual organisms o Fossils o Organisms about which little is known regarding their reproduction Limitations of the BSC Speciation Dependent on o Reproductive isolation o Genetic divergence Reproductive 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 mate Post 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 Behavioral Is gametic isolation a pre zygotic or post zygotic isolating mechanism 1 Pre zygotic 2 Post zygotic 3 4 It depends on the species or whether it acts pre or post zygotically It can be either depending on the time of year Concept 24 2 Speciation can take place with or without geographic separation Speciation can occur in two ways o Allopatric speciation o Sympatric speciation Which of the following is not considered a requirement for speciation 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 Establishing Reproductive Isolation Sympatric Same Country Speciation Speciation that takes place in geographically overlapping populations Polyploidy 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 species Allopolyploidy Plant 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 12 b 14 c 16 d 28 use add method to add diploid numbers from both species e 56 Sympatric Speciation in Progress The Apple Maggot Fly Hawthorn Flies In cichlid fish Sympatric speciation has resulted from nonrandom mating due to sexual selection Example of Stability in Hybrids Which of the following is the first step in the process of allopatric speciation Interspecies contact a Genetic Drift b c 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 species b Ecological isolation c Temporal isolation d Polyploidy Concept 24 3 Hybrid Zones Provide Opportunities to Study Factors that Cause Reproductive Isolation Possible Outcomes for Hybrids The Breakdown of Reproductive Barriers Fusion Chapter 25 The History of Life on Earth Early Earth The Earth is about 4 6 billion years old o Radiometric dating of meteorites moon rocks Life arose about 3 8 billion years ago o Chemical traces in rock 3 8 BYA o Fossil bacteria in rocks 3 5 BYA No spontaneous generation now but must have happened then Conditions on Early Earth Atmosphere o CO2 CH4 NH3 H2S H2O o No free oxygen Abundant Energy to drive reaction o Frequent storms with much lightening o Frequent volcanic eruptions o Frequent meteor impacts o Ultraviolet light from the sun Testable hypotheses explaining the origin of life 1 Abiotic synthesis of small organic molecules 2 Joining these molecules into polymers 3 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 organic material without oxygen Early Earth elements Alternative Hypotheses 1 First organic compounds may have been synthesized near hydrothermal vents 2 Extraterrestrial origin meteorites ice space Abiotic 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 water Oxygen has a influence on the formation of complex organic molecules because 1 Positive it increases metabolism 2 Positive it acts as a coenzyme 3 Negative it prevents photosynthesis 4 Negative it is highly reactive The Chicken or the Egg Now Then DNA RNA Protein Need proteins to synthesize more DNA 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 information Concept 25 2 The fossil record documents the history of life Fossils document the history of life Sedimentary strata reveal the relative ages of fossils o Fossils near surface more recent o Deeper fossils more ancient Fossils records shows great changes in organisms through time Dating of Fossils Order of fossils in rock strata tells us the sequence in which they were laid down This provides relative ages not absolute dates Radiometric Dating Can determine absolute ages of fossils o Radioactive isotopes decay into a daughter isotope at a fixed rate o life amount of time it takes for 50 of an isotope to decay When a certain rock formed it contained 12 mg 40K The rock now contains 3 mg
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