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SB5 Chapters 14, 15, & 16 Chapter 15 All organisms have evolutionary adaptations Inherited characteristics that enhance their ability to survive and reproduce Example: The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment ▪ Large, webbed feet help propel the bird through water at high speeds ▪ A streamlined shape, large tail, and nostrils that close are useful for diving ▪ Specialized salt-secreting glands manage salt intake while at sea Aristotle and the Judeo-Christian culture believed that species were fixed. Fossils suggested that life forms change. Early 1800s Jean Baptiste Lamarck, a French invertebrate specialist, studied fossils to learn about different invertebrates. He was surprised by the similarities between the existing animals that he studied. He also noticed that fossils showed traits changing over time. For example, he noticed that giraffes’ necks were getting longer and longer from generation to generation. He theorized that this trait developed as giraffes stretched their necks for higher leaves to avoid competition with shorter animals. English naturalist who sailed on the HMS Beagle Mission of 5-yr voyage – map the coast of South America Darwin’s role – collect biological and geological samples Inspirational reading – Charles Lyell’s book proposing that the earth was millions of years old Similarities between living things and fossil organisms Diversity of life on the Galapagos Islands, such as blue-footed boobies and giant tortoises ▪ Visited 4 islands in the chain; noticed each island had slightly different varieties of animal ▪ Discovered many new species that were not found in S America Darwin became convinced that the Earth was old (as Lyell said in the book he was reading). He suggested that the Earth is continually changing. He concluded that living things also change or evolve over generations. He also stated that living species descended from earlier life-forms: descent with modification. He believed that new species could appear gradually through small changes in traits. He was unsure how this process would work. He turned to animal breeders for help. Breeders selected desired traits in pigeons and bred them. (We called this selective breeding in the Genetics Unit.) Darwin called this practice artificial selection. Darwin explained that if humans could change species by artificial selection, then perhaps nature could do the same thing over time. He concluded that this is how new species develop naturally over time…natural selective breeding. Darwin proposed that natural selection is the mechanism of evolution. Natural selection – NATURE’s way of selective breeding Four Basic Principles: Organisms in a population show variations. Variations can be passed down to offspring. Organisms produce more offspring than resources can support. Variations that increase survival also increase the likelihood of reproduction and inheritance. The favorable characteristics are passed down to offspring who are likely to survive due to the favorable characteristic. Population size increases due to favorable characteristics in offspring. Over time, whole populations change to include the favorable characteristic. Enough changes can give an entirely new species. Natural Selection Fossil Record, Biogeography, Comparative Anatomy, Comparative Embryology, and Molecular Biology Fossils offer evidence for evolution: Hominid skull Petrified trees Fossilized organic matter in a leaf Scorpion in amber • Many fossils link early extinct species with species living today – These fossilized hind leg bones link living whales with their land-dwelling ancestors Continental drift is the slow, incessant movement of the Earth’s crustal plates on the hot mantle. Eurasian Plate North American Plate African Plate Pacific Plate Nazca Plate South American Plate Split developing Indo-Australian Plate Antarctic Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) CENOZOIC Eurasia Africa MESOZOIC Antarctica PALEOZOIC Millions of years ago Crustal plates have shifted over millions of years to significantly change the layout of the globe. India South America Laurasia Homologous structures: anatomically similar structures inherited from a common ancestor Forelimbs of vertebrates are adapted for different uses, but they have the similar bones. Human Cat Whale Bat Vestigial structure: reduced forms (smaller) of functional structures in other organisms Example: Human appendix; structure is important for digestion in many mammals but of limited use in humans and apes Vertebrate embryos exhibit homologous structures during certain phases of development. Example: Pharyngeal pouches Develop into gills in fish Develop into ears, jaws, and throats in mammals, birds, and reptiles Darwin’s idea of natural selection and the evidence of comparative anatomy has lead scientists to observe evolution in action. Example: Evolutionary adaptations have been observed in many populations of birds and insects Camouflage adaptations Example: Insecticide resistance Insecticide application Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Modern synthesis of evolution ideas connects Darwin’s theory of natural selection with population genetics So…what’s population genetics? Populations are the units of evolution. A species is a group of populations whose individuals can interbreed and produce fertile offspring. Human populations tend to concentrate locally, as this satellite photograph of North American shows Microevolution is change in a population’s gene pool over time. A gene pool is the total collection of genes in a population at any one time. Microevolution involves a change in the relative frequencies of alleles in a gene pool. ▪ Example: Bug color ratio (frequency of alleles) What is the ratio of graybrown to yellow-brown to dark brown bugs? The Hardy-Weinberg principle states that evolution (change in the frequency of alleles) will not occur unless acted upon by forces that cause change. Connection to meiosis: the shuffling of genes (crossing over, etc.) during sexual reproduction does not alter the proportions of different alleles in a gene pool When allelic frequency remains constant, a population is in Hardy-Weinberg equilibrium. We can map alleles in a population to observe if Hardy-Weinberg equilibrium exists. The population is very large The population is isolated Mutations do not alter the gene pool Mating is random All individuals are equal in reproductive success Hardy (English mathematician) and Weinberg (German physician) developed an equation to show mathematically that random mating will not cause changes in allele frequencies. EQUATION: p2 + 2pq + q2 = 1 frequency of dominant + frequency of recessive = 1 p+q=1 p2 = pp= homozygous dominant genotype pq = heterozygous genotype q2 = qq = homozygous recessive genotype EQUATION: p2 + 2pq + q2 = 1 Remember: p +q = 1 Assume you have the following genotypes in gold fish crackers: FF, Ff, and ff. Mating is random. Any fish could mate with any other fish. F and f are the only two alleles from fish color. F = brown; FF and Ff are brown fish. f = gold; ff = gold fish EQUATION: p2 + 2pq + q2 = 1 Remember: p +q = 1 Example: Let’s say that you’ve calculated that you have 16% ff fish. We can use the equation to calculate the frequency of the homozygous dominant and the heterozygous alleles. Solved on whiteboard in class! Fishy Frequencies Lab in Class! Microevolution: change in frequencies of alleles in a gene pool Example: if blue eyes began to disappear in the population. Remember, the Hardy-Weinberg principle says that reproduction and variations in meiosis won’t cause microevolution. Microevolution only occurs when a force acts on the population to cause the changes. Genetic drift is a change in a gene pool due to chance. In large populations, enough organisms are reproducing with random selection of alleles to prevent changes in the gene pool. In smaller populations, random selections could reduce the diversity by mere chance. Extreme genetic drift can cause the bottleneck effect. Bottleneck Effect: a population dwindles to a very low number and then rebounds Small population gives little diversity. Little diversity reproduces little diversity. Example: African cheetahs – so genetically similar that they appear to be inbred Original population Bottlenecking event Surviving population Founder Effect: a small segment of the population moves to a separate area Separate segment may have traits that are uncommon to the original population Uncommon traits become common in offspring in the new population Can result in large genetic variability from one segment of the population to another Natural selection acts to select individuals who are the best adapted for survival and reproduction. Those who lack these traits often die before reproducing. Natural selection results in the accumulation of traits that adapt a population to its environment If the environment should change, natural selection would favor traits adapted to the new conditions. Phenotypic variation may be environmental or genetic in origin. Only genetic changes will result in evolutionary adaptations as only genes are passed to offspring. Example: Environment may cause a tan, but tans are not passed down to offspring. Population skin color will only become darker if darker skin color genes become more common in offspring. Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Diversifying selection Directional Selection: extreme version of a trait makes the organism more fit for survival and reproduction Example: Peppered moth – until mid-1850s moths were light colored in England. By early 1900s, nearly all were dark colored. The darker the moth, the better it blended into the sooty surroundings of the industrial pollution Luck y for the moth species that it had a darker allele to begin favoring. Low genetic variability may reduce the capacity of a species to survive as humans continue to alter the environment. Example: African cheetah – diversity was decreased by bottleneck effect which resulted in fewer alleles (as if they’d been inbred) Fewer alleles = reduced capacity to adapt to environmental challenges Sexual selection leads to the evolution of secondary sexual characteristics These may give individuals an advantage in mating. Natural selection cannot fashion perfect organisms. Historical constraints Adaptive compromises Chance events Availability of variations The excessive use of antibiotics is leading to the evolution of antibioticresistant bacteria Example: Mycobacterium tuberculosis They aren’t perfect, but the are perfectly annoying to the CDC.