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EVOLUTION & SPECIATION VOCABULARY REVIEW • EVOLUTION – CHANGE OVER TIME • NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE. – A.K.A. “SURVIVAL OF THE FITTEST” Charles Darwin • Wrote in 1859: “On the Origin of Species by Means of Natural Selection” • Two main points: 1. Species were not created in their present form, but evolved from ancestral species. 2. Proposed a mechanism for evolution: NATURAL SELECTION Natural Selection • Individuals with favorable traits are more likely to leave more offspring better suited for their environment. • Also known as “Differential Reproduction” • Example: English peppered moth (Biston betularia) - light and dark phases Darwin’s 5 points 1. Population has variations. 2. Some variations are favorable. 3. More offspring are produced than survive 4. Those that survive have favorable traits. 5. A population will change over time. Artificial Selection • The selective breeding of domesticated plants and animals by man. • Question: What’s the ancestor of the domesticated dog? • Answer: WOLF Evidence of Evolution 1. Biogeography: Geographical distribution of species. 2. Fossil Record: Fossils and the order in which they appear in layers of sedimentary rock (strongest evidence). NEW VOCABULARY • POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED • GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION Gene Pool Combined genetic info. of all members Allele frequency is # of times alleles occur Variation in Populations 2 processes can lead to this: Mutations change in DNA sequence Gene Shuffling – from sexual reproduction a. Bottleneck Effect • Genetic drift (reduction of alleles in a population) resulting from a disaster that drastically reduces population size. • Examples: 1. Earthquakes 2. Volcano’s • • • Genetic drift can cause big losses of genetic variation for small populations. It reduces genetic variation. Population bottlenecks occur when a population’s size is reduced for at least one generation. This is illustrated by the bags of marbles shown below, where, in generation 2, an unusually small draw creates a bottleneck • Reduced genetic variation means that the population may not be able to adapt to new selection pressures, such as climatic change or a shift in available resources, because the genetic variation that selection would act on may have already drifted out of the population. • An example of a bottleneck: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. Genetic Drift changes populations……. • Random change in allele frequency causes an allele to become common • Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population • Non-random mating: inbreeding and assortive mating (both shift frequencies of different genotypes) • Assortative mating occurs when individuals select mates non-randomly from within their population, on the basis of a trait that both they and their mates express. Founder Effect • Genetic drift resulting from the colonization of a new location by a small number of individuals. • Results in random change of the gene pool. • Example: 1. Islands (first Darwin finch) Five Mechanisms of Microevolution 1. Islands (first Darwin finch) 2. Gene Flow: The gain or loss of alleles from a population by the movement of individuals or gametes. • Immigration or emigration. • Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations) Five Mechanisms of Microevolution 3. Mutation: Change in an organism’s DNA that creates a new allele. 4. Non-random mating: The selection of mates other than by chance. 5. Natural selection: Differential reproduction. Modes of Action • Natural selection has three modes of action: 1. Stabilizing selection 2. Directional selection 3. Diversifying selection Number of Individuals Small Large Size of individuals 1. Stabilizing Selection • Acts upon extremes and favors the intermediate. Number of Individuals Small Large Size of individuals 2. Directional Selection • Favors variants of one extreme. Greyhounds Bred for speed Number of Individuals Small Large Size of individuals 3. Diversifying Selection • Favors variants of opposite extremes. Number of Individuals Small Large Size of individuals Speciation • The evolution of new species. Reproductive Barriers • Any mechanism that impedes two species from producing fertile and/or viable hybrid offspring. • Two barriers: 1. Pre-zygotic barriers prevent fertilization 2. Post-zygotic barriers prevents fertilized egg from developing into a fertile adult 1. Pre-zygotic Barriers a. Temporal isolation: Breeding occurs at different times for different species. b. Habitat isolation: Species breed in different habitats. c. Behavioral isolation: Little or no sexual attraction between species. 1. Pre-zygotic Barriers d. Mechanical isolation: Structural differences prevent gamete exchange. e. Gametic isolation: Gametes die before uniting with gametes of other species, or gametes fail to unite. 2. Post-zygotic Barriers a. Hybrid inviability: Hybrid zygotes fail to develop or fail to reach sexual maturity. b. Hybrid sterility: Hybrid fails to produce functional gametes. c. Hybrid breakdown: Offspring of hybrids are weak or infertile. • One oft-cited example of a postzygotic mating barrier occurs when horses and donkeys, • two different species, interbreed to produce mules. Mules, as a hybrid offspring, are generally robust organisms. However, the genetic incompatibility of the horse and the donkey result in sterility in the mule. • Because mules are infertile, gene flow between the horse and donkey is effectively blocked, even though they are able to produce hybrid offspring. • Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment Sexual selection • Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism • Sexual dimorphism is a phenotypic difference between males and females of the same species. Evolution of Populations Occurs when there is a change in relative frequency of alleles How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant mutation! How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant Generation 4: 0.12 not resistant 0.88 resistant Phenotype Expression • Depends on how many genes control that trait Single-Gene vs. Polygenic Traits Single-Gene: 2 Distinct Phenotypes (EG: tongue rolling) Polygenic: Many Phenotypes Allele Frequencies Natural Selection Single Gene Traits Genetic Drift Polygenic Traits Directional Selection Stabilizing Selection Disruptive Selection Natural Selection on Polygenic Traits • Shifts to middle range • Shifts to 2 extremes • Shifts to 1 extreme Conditions needed for Genetic Equilibrium Hardy-Weinberg Principle • The concept that the shuffling of genes that occur during sexual reproduction, by itself, cannot change the overall genetic makeup of a population. Hardy-Weinberg Principle • This principle will be maintained in nature only if all five of the following conditions are met: 1. 2. 3. 4. 5. Very large population Isolation from other populations No net mutations Random mating No natural selection Hardy-Weinberg Principle • Remember: If these conditions are met, the population is at equilibrium. • This means “No Change” or “No Evolution”. Macroevolution • The origin of taxonomic groups higher than the species level. Microevolution • A change in a population’s gene pool over a secession of generations. • Evolutionary changes in species over relatively brief periods of geological time. Five Mechanisms of Microevolution 1. Genetic drift: Change in the gene pool of a small population due to chance. • Two examples: a. Bottleneck effect b. Founder effect SPECIATION • THE FORMATION OF NEW SPECIES • AS NEW SPECIES EVOLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED • REPRODUCTIVE ISOLATION – MEMEBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING. 3 ISOLATING MECHANISMS…….. • BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS) • GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL) • TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES. Table 23.1a Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically. Liger Result of male lion and female tiger mating in captivity. Offspring are infertile. Table 23.1b Fig. 23.6 Four species of leopard frogs: differ in their mating calls. Hybrids are inviable. Allopatric Speciation • Induced when the ancestral population becomes separated by a geographical barrier. • Example: Grand Canyon and ground squirrels These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation. Hawaiian Honeycreepers An example of adaptive radiation – these species all diverged from a common ancestor (founder species) FOUNDER SPECIES Adaptive Radiation • Emergence of numerous species from a common ancestor introduced to new and diverse environments. • Example: Darwin’s Finches SPECIATION IN DARWIN’S FINCHES • SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY: - FOUNDING OF A NEW POPULATION, - GEOGRAPHIC ISOLATION which led to - REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION. Evidence of Evolution 1. Fossil Record 2. Geographic Distribution of Living Species 3. Homologous Body structures 4. Similarities in Embryology Evidence of Evolution Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time Convergent Evolution • Species from different evolutionary branches may come to resemble one another if they live in very similar environments. • Example: 1. Ostrich (Africa) and Emu (Australia). 2. Sidewinder (Mojave Desert) and Horned Viper (Middle East Desert) Flying Squirrel Sugar Glider Marsupial Mammals Convergent Evolution and Analogous Structures Placental mammals Mammalia Rat like common ancestor Review Big Question!!! How did life arise on the big blue planet?? Scientists attempt to answer this question scientifically. Relative Dating versus Absolute Dating Relative Dating • Can determine a fossil’s relative age • Performed by estimating fossil age compared with that of other fossils • Drawbacks – provides no info about age in years Absolute dating • Can determine the absolute age in numbers • Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain • Drawbacks - part of the fossil is destroyed during the test Carbon-14 Dating Fossil Formation Big Bang Theory A cosmic explosion that hurled matter and in all directions created the universe 10-20 billion years ago Evidence it explains why distant galaxies are traveling away from us at great speeds Cosmic radiation from the explosion can be observed The Big Bang theory probably will never be proven; consequentially, leaving a number of tough, unanswered questions. What was early earth like? Earth was Hot!! Little or no oxygen Gasses in atmosphere: Hydrogen cyanide (poison to you!) Hydrogen sulfide Carbon dioxide Carbon monoxide Nitrogen So how did the earth get oxygen? Some of that oxygen was generated by photosynthetic cyanobacteria Some came from the chemical separation of water molecules into oxygen and hydrogen. Oxygen drove some life forms to extinction Others evolved ways of using oxygen for respiration How did life begin? Miller and Urey’s Experiment Passed sparks through a mixture of hydrogen methane ammonia and water This produced amino acids – the building blocks of life Miller’s experiment suggests that lightning could have produced amino acids How can simple amino acids result in life? There are 3 theories 1. Formation of microspheres Large organic molecules can sometimes form tiny proteinoid microspheres Store and release energy, selectively permeable membranes, may have acquired more characteristics of living cells nd 2 Hypothesis for Life Evolution of RNA to DNA • RNA was assembled from simple organic molecules in a primordial soup • RNA was able to replicate itself and eventually form DNA • Not scientifically proven to be possible rd 3 Theory of Life Endosymbiotic theory eukaryotic cells arose from living communities formed by prokaryotic organisms Ancient prokaryotes entered primitive eukaryotic cells and remained there as organelles