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AP Test Evolution/Classifcation Review Evolution • Evolution is genetic change in a population over time. • Charles Darwin was the first scientist to propose the theory of evolution, in 1859. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin observed: – similarities between living and fossil organisms – the diversity of life on the Galápagos Islands, such as finches (birds) and giant tortoises Figure 13.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin concluded that: – The Earth was old and constantly changing (4.6 billion years old) – Living things also change (evolve) over generations. – Living things are related to animals and plants that used to exist but are now extinct. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Evidence for Evolution • Fossils • Biogeography • Comparative Anatomy • Comparative Embryology • Molecular Biology Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Natural Selection • Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted • Aka: survival of the fittest (giraffe example) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin saw natural selection as the basic mechanism of evolution – As a result, the proportion of individuals with favorable characteristics increases – Populations gradually change in response to the environment – Phenotypes that are better reproduce more, eventually, better genotypes become more common. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment – This is called artificial selection – Example of artificial selection in plants: five vegetables derived from wild mustard Figure 13.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.7 Microevolution • A gene pool is the total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool • New mutations are constantly being generated in a gene pool, by accident or as a response to environmental changes. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings What causes evolution? • Genetic drift • Bottleneck Effect • Founder Effect • Gene Flow • Mutation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Drift • Genetic drift is a change in a gene pool due to chance – Genetic drift can cause the bottleneck effect: an event that drastically reduces population size (fire, flood, earthquake) Original population Bottlenecking event Surviving population Figure 13.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic drift… • If a population is very diverse and something bad happens, at least a few individuals will survive. • These individuals will then reproduce and the species will evolve, or change. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – The founder effect is when some individuals leave a population and start living somewhere new. – Only a few people or animals leave, and the new population will be closely related to due lack of genetic diversity. Figure 13.11B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Gene flow can change a gene pool due to the movement of genes into or out of a population (new organisms move in or leave) • Mutation changes alleles, these are random changes in DNA that can create new proteins or new characteristics. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.8 Hardy-Weinberg Equilibrium • Showing that evolution has to happen by showing that characteristics in nature are always changing... • Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool • Populations are always evolving and not usually in equilibrium. Figure 13.8A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.10 Five conditions are required for HardyWeinberg equilibrium • 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 • ***This does not happen in nature! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Equation • p2 + 2pq + q2 = 1 • p+q=1 • p = frequency of the dominant allele in the population (A) q = frequency of the recessive allele in the population (a) p2 = percentage of homozygous dominant individuals (AA) q2 = percentage of homozygous recessive individuals (aa) 2pq = percentage of heterozygous individuals (Aa) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings MACROEVOLUTION 15.1 The fossil record chronicles macroevolution • Macroevolution consists of the major changes in the history of life – The Earth is 4.6 billion years old – Life appeared 3.8 billion years ago: as single celled prokaryotic bacteria – Around 500 million years ago, simple marine animals and plants had evolved Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.2 Radiometric Dating • Radiometric (or carbon) dating is based on the measurement of certain radioactive isotopes • Scientists can measure how much carbon is left in a fossil, and can then determine how old that fossil is. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.6 Adaptations • A structure that evolved in one context and was later adapted to another function is referred to as exaptation. – Example: Dinosaurs evolved feathers as insulation against extreme temperatures, as birds evolved from small dinosaurs, feathers changed through natural selection to give flight. Figure 15.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.9 Phylogeny • Phylogeny is the evolutionary history of a group of organisms. • Biologists construct phylogenic trees, which are diagrams that trace evolutionary relationships. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.10 Systematists classify organisms by phylogeny • Reconstructing phylogeny is part of systematics, the study of biological diversity and classification. • Taxonomists assign a two-part name to each species (binomial nomenclature) – The first name, the genus, covers a group of related species (but they can’t breed!) Ex: Homo – The second name refers to a species within a genus Ex: sapiens – Another Example: Canis familiaris (italics, genus capitalized, species not) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A review of taxonomy • Taxonomy is the system of classifying living organisms. • Kings = Kingdom (Anamalia) • Play = Phylum (Chordata) • Chess = Class (Mammalia) • On = Order (Primates) • Funny = Family (Hominidae) • Green = Genus (Homo) • Squares = Species (sapiens) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A newer system recognizes two basically distinctive groups of prokaryotes – The domain Bacteria – The domain Archaea • A third domain, the Eukarya, includes all kingdoms of eukaryotes BACTERIA Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ARCHAEA EUKARYA Earliest organisms Figure 15.14B 15.11 Homology vs. Analogy • Homologous structures are evidence that organisms have evolved from a common ancestor (human arm, whale flipper) • In contrast, analogous similarities are evidence that organisms from different evolutionary lineages have undergone convergent evolution (shark and dolphin) – Their resemblances have resulted from living in similar environments – Example: A bat wing and a bee wing (they are NOT homologous, they are analogous) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.12 Molecular Biology • Systematists increasingly use molecular techniques to Human Chimpanzee Gorilla Orangutan – classify organisms – develop phylogenetic hypotheses – Protein sequences, DNA, and RNA of different organisms are compared to determine relationships. Figure 15.12B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15.13 Cladistic Analysis • Clades are evolutionary branches that consist of a common ancestor and all the organisms that evolved from it. • A phylogenic tree based on cladistic analysis is called a cladogram. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Quick Review Key terms • Phylogeny is the evolutionary history of a species or group of species. • Systematics is the analytical approach to understanding the diversity and relationships of organisms. • Molecular Systematics compares DNA and RNA of different organisms to determine evolutionary relationships Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive Barriers • Reproductive Barriers prevent members of different species from producing viable, fertile offspring. (there are 2 types) • 1. Prezygotic barriers: impede mating or hinder fertilization if mating does occur (BEFORE zygote forms) • 2.Postzygotic barriers: prevent a hybrid zygote from developing into a viable, fertile adult (AFTER zygote forms) (Ex: Mule) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Prezygotic Barriers • 1. Habitat isolation: 2 species live in different habitats and don’t see each other • 2. Temporal isolation: 2 species breed at different times of the day or year • 3. Behavioral isolation: courtship rituals are species specific, and don’t attract other species • 4. Mechanical isolation: the sexual pieces don’t fit together • 5. Gametic isolation: even if sex occurs, the egg and sperm can’t meet Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Postzygotic barriers • 1. Reduced hybrid viability: hybrid babies die before reaching reproductive age • 2. Reduced hybrid fertility: hybrid babies are sterile and can’t reproduce • 3. Hybrid breakdown: first generation babies can breed, but their children are infertile (F2) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How do new species form? • Allopatric speciation: “other country,” a population is geographically divided into 2 isolated subpopulations, which eventually become 2 new species • Sympatric speciation: “same country,” 2 new species develop in the same area – Mutations such as polyploidy (extra set of chromosomes) – Habitat differentiation – Sexual selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Adaptive Radiation • Adaptive radiation: the evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges • Example: Hawaiian plants Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Extras • Punctuated equilibrium: lots of new species appear all at once in history (Cambrian explosion) • Kin Selection: refers to strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to their own survival. (Altruistic Behavior) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings