Chapter 13

Chapter 13 - Slide 1 Chapter 13 How Populations Evolve Why...

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Unformatted text preview: Slide 1 Chapter 13: How Populations Evolve Why is life on earth so diverse? Slide 2 Evolution • Changes occurring, over time, in a population (NOT AN INDIVIDUAL) Slide 3 Evolutionary adaptations • Inherited changes that enhance an organism’s ability to survive and reproduce in a particular environment Slide 4 Slide 5 Booby Slide 6 Booby adaptations • Webbed feet: propelling birds through the water at high speeds • Streamlined body: reduces friction in water • Wedged shaped tail: allows quick stopping in water • Closeable nostrils: prevents water from entering when diving • Glands: oil for waterproofing and salt regulation Slide 7 Adaptations are often a trade­off • Remember, evolutionary adaptations need to allow the organism better survival possibilities, therefore promoting reproduction • Booby’s big feet: Advantage? Disadvantage • Adaptations that allow an organism to survive longer/better will always win Slide 8 Slide 9 Most famous evolutionary scientist? Charles Darwin But…Darwin wasn’t first Slide 10 • ~500 B.C. Greek philosophers suggested life may have arisen from as simple life forms in water • Aristotle held the belief that species were fixed – great influence on western culture • 1700s: Fossil evidence lead scientists to believe earth is much older than 6,000 years And then there was Lamarck Slide 11 • In the early 1800s Jean Baptiste Lamarck was among the first to publicly speculate that there was a relationship between fossils and living organisms • Evolution • Unfortunately, he is mostly remembered for being wrong about the mechanism of evolution Lamarck’s mechanism Slide 12 • He based his theory on “use or disuse” • He though that body parts changed based on their use, and that these changes were passed on to offspring • Example: Giraffe necks Why such a long neck? Slide 13 Slide 14 Slide 15 Disadvantages? Slide 16 Why was Lamarck important? • Thought that species changed through their interaction with their environment • Set up the modern concept of evolution • Paved the way for Darwin to get the mechanism right Slide 17 Slide 18 Charles Darwin and the voyage of the HMS Beagle Great Britain Europe Asia North America ATLANTIC OCEAN PACIFIC OCEAN PACIFIC OCEAN Pinta Marchena Santiago Pinzón Fernandina Isabela 0 0 40 km Daphne Islands Santa Santa Cruz Fe Florenza 40 miles Australia Genovesa Equator San Cristobal Española PACIFIC OCEAN Equator South America Andes The Galápagos Islands Africa Cape of Good Hope Cape Horn Tierra del Fuego Tasmania New Zealand Galapagos Islands Slide 19 Galapagos Islands Slide 20 • Contain hundreds of species that are found nowhere else on earth (endemic) • Darwin found many uniques species that were similar to each other, but had slight variations between islands (e.g. Finches) More Darwin Slide 21 • 1840s – wrote a long essay on what he found (didn’t publish) • 1850s – Darwin was sent a summary of George Wallace’s work • 1858 – Darwin allowed a colleague to present his work (along with Wallace’s) at a conference • 1859 – Published his book, On the Origins of Species by the means of Natural Selection “Descent with modification” • This is an important area where Darwin differed from Lamarck (but he was correct) • All species are related through a common ancestor • The descendents moved into diverse environments • In each environment, the descendents began to accumulate changes • These changes were modifications (adaptations) that allowed them to better survive intheir environment Slide 22 Natural Selection Slide 23 • Darwin’s mechanism of evolution • Darwin made 3 key observations that lead to the idea of natural selection 1. Overproduction of offspring 2. Variation in characteristics of individuals within a population 3. The characteristics that vary are passed on to offspring Natural Selection (cont.) • Darwin suggested that traits that were favorable were selected for by the environment • These traits show up more and more in each generation and accumulate over time. Slide 24 Natural Selection (cont.) Population with varied inherited traits Slide 25 Natural Selection (cont.) Elimination of individuals with certain traits Slide 26 Natural Selection (cont.) Reproduction of survivors Slide 27 Slide 28 Natural Selection (cont.) African wild dog Coyote Wolf Thousands to millions of years of natural selection Ancestral canine Fox Jackal Artificial Selection Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Slide 29 Artificial Selection (cont.) Slide 30 Evidence for Evolution • Fossils • Biogeography • Comparative anatomy • Vestigial organs • Comparative embryology Slide 31 Fossils • Preserved remnant or impression of an organism that lived in the past • It is possible to document the changes in organisms over time by looking at fossils • There are several different types of fossils Slide 32 Hard parts often remain Slide 33 Petrification: A process of fossilization in which dissolved minerals replace organic matter. Slide 34 Casts Slide 35 Trace fossils Slide 36 Slide 37 Some fossils retain organic matter 100% Preserved Slide 38 Frozen Slide 39 Sedimentary Rocks Slide 40 Fossil Record Slide 41 • Younger layers are always on top of older ones • The age of fossils can be correlated to what layer they are in (i.e. how deep) • The ordered array of how fossils appear in sedimentary rock is called the fossil record Fossil Record (cont.) Slide 42 • The fossil record demonstrates the historical sequence of evolution • The oldest known fossils are approximately 3.5 billion years old and are of prokaryotes (any cellular organism that has no nuclear membrane, no organelles in the cytoplasm except ribosomes, and has its genetic material in the form of single continuous strands forming coils or loops, characteristic of all organisms in the kingdom Monera, as the bacteria and blue­green algae or An organism of the kingdom Prokaryotae, constituting the bacteria and cyanobacteria, characterized by the absence of a nuclear membrane and by DNA that is not organized into chromosomes.) • As you go up in layers, you find the sequence of evolution Fossil Record (cont.) Slide 43 Biogeography • Geographical distribution of species Slide 44 Comparative Anatomy Slide 45 • The comparison of body structures in different species • Homology: describes characteristics that are similar in different species because of a common ancestor Slide 46 Comparative Anatomy (cont.) Human Cat Whale Homologous Structures Bat Vestigial Organs Slide 47 • Remnants of structures that served important functions in an organism’s ancestors • Current function could be marginal, or non existant Vestigial Organs Slide 48 Comparative Embryology • The comparison of early stages of development in different species Slide 49 Comparative Embryology (cont.) Pharyngeal pouches Post-anal tail Chick embryo Human embryo Slide 50 Molecular Biology • Scientists can use molecular biology to compare species at the molecular level • DNA • Protein • The more similar two organisms are at the molecular level, the more closely related Slide 51 Molecular Biology (cont.) Slide 52 Natural Selection in Action • Can we see evolution happening today? • YES Slide 53 Slide 54 Chromosome with gene conferring resistance to pesticide Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Pesticide application Survivor Slide 55 Three key points of natural selection 1. It is an editing process (it does not create new individuals) 2. It is contingent on time and place 3. Significant changes can occur in a population in a short time Population Genetics Slide 56 • Population – group of individuals of the same species living in the same space at the same time • Species ­ group of populations whose members are capable of interbreeding and producing fertile offspring Slide 57 Population Genetics Slide 58 • Combination of ideas from Darwin and Mendel • The study of genetic changes within a population • Gene pool – total of all genetic combinations in a population • • Do you remember what an allele is? A: Any of the possible forms in which a gene for a specific trait can occur. In almost all animal cells, two alleles for each gene are inherited, one from each parent. Paired alleles (one on each of two paired chromosomes) that are the same are called homozygous , and those that are different are called heterozygous . In heterozygous pairings, one allele is usually dominant, and the other recessive. Complex traits such as height and longevity are usually caused by the interactions of numerous pairs of alleles, while simple traits such as eye color may be caused by just one pair. • When the allelic frequency changes over time, it is called microevolution. Hardy­Weinberg Equilibrium Slide 59 • The genetic make­up of a population does not change with sexual reproduction • An outside force is needed • Hardy­Weinberg describes the allelic frequencies in a population • If allelic frequencies change over time, this indicates that the population is evolving Slide 60 Hardy­Weinberg Equilibrium (cont) • There are five basic conditions that must be met for a population to be at Hardy­Weinberg equilibrium (non­ evolving) 1. Very large population 2. No gene flow 3. No mutations 4. Random mating 5. No natural selection • VERY IMPORTANT: These conditions are never met in nature Slide 61 Three contributing factors to evolution 1. Natural Selection 2. Gene flow 3. Genetic drift Genetic Drift Slide 62 • Occurs when the gene pool of a population changes by chance • Occurs when the size of a population “shrinks” so that the remaining members are not representative of the original • Two situations which result in smaller population 1. Bottleneck effect 2. Founder effect Slide 63 Bottleneck Effect Original population Bottlenecking event Surviving population Founder Effect Slide 64 Endangered Species Slide 65 Variation Slide 66 Variation Slide 67 • Individuals in sexually reproducing populations always exhibit variation Variation at the molecular level Slide 68 Not all variation is heritable Slide 69 Slide 70 Mutations in gamete producing cells are heritable Mutations • Most mutations are harmful • When a mutation is good, it is usually because it happens in a changing environment Slide 71 HIV Slide 72 Chromosomal Mutations Slide 73 Slide 74 Rapid Mutations in Microorganisms Slide 75 Natural Selection and Populations • There are three main ways that natural selection affects the phenotypes within a population: 1. Stabilizing Selection 2. Directional Selection 3. Disruptive Selection Slide 76 Natural Selection and Populations Frequency of individuals Original population Phenotypes (fur color) Stabilizing Selection Original population Evolved population Stabilizing selection Slide 77 Directional Selection Directional selection Slide 78 Disruptive Selection Disruptive selection Slide 79 Sexual Dimorphism • When males and females of a species differ in secondary sex characteristics • In vertebrates, males are usually the showier sex! • Examples: Size Difference Male adornment (Plumage, lion’s mane, antlers, etc.) Slide 80 Sexual Selection • Process that leads to sexual dimorphism • Darwin considered it separate from natural selection • Two types: 1. Intrasexual selection (within the same sex) 2. Intersexual selection (between the sexes) Slide 81 Intrasexual Selection Slide 82 Intersexual Selection Slide 83 Slide 84 Natural selection cannot fashion a perfect organism! • Why? 1. Organisms are limited by historical constraint 2. Adaptations are often compromises 3. Chance and natural selection interact 4. Selection can only edit existing variations What is your biological role? Getting your genes into the next generation! Slide 85 ...
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