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Transcript
4/2/2017 15-1 The Puzzle of Life’s Diversity Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. = Change over time = Change in the frequency of an allele in a population Evolution is not something that only happened in the past; it is still going on. It does not happen to individuals, it happens to populations. Charles Darwin The Galapagos Islands greatly influenced Darwin’s ideas. Observed: • Marine fossils atop mountains • Organisms have variations based upon environment • Similarities between extinct fossils & modern life • Organisms seem remarkably well suited for their environment Darwin found 13 species of finches on Galapagos Island. Each group of finches had its own niche (an organism’s habitat and its role in that habitat). 15-2 Ideas That Shaped Darwin’s Thinking Most people in Darwin’s day believed that Earth was only a few thousand years old, and that all of today’s species had existed unchanged since their creation. The shape of a tortoise’s shell corresponded to its habitat. • Tortoises on hot, dry islands had long necks and shells that curved open around the neck and legs. • On islands with rich vegetation, tortoise’s had a shorter neck and dome-shaped shell. 1 4/2/2017 •Acquired Inheritance: Early theory where organisms could acquire and pass traits after birth •Cause: environmental changes forced individuals to change - organisms strive to improve themselves - unused body structures wasted away and most used structures develop •Early Belief: Giraffes & Long Necks –Long necks are result of stretching to reach leaves –Extra length was passed on to offspring •Problem: Traits acquired after fertilization cannot be passed to offspring 15.3 Darwin Presents His Case The Theory of Natural Selection • Darwin mulled over his ideas for 25 years before publishing • Alfred Wallace sent Darwin an essay containing similar ideas; they presented their ideas together • Darwin published his book 18 months later (1859) Natural Variation • Defined: Inherited traits that make an individual different from others • Natural variation is found in all types of organisms. • Much of this variation can be inherited Artificial Selection • Defined: Humans select (not naturally) traits thought to be advantageous • Humans created diversity choosing specific traits to breed –Dogs, Crops, Livestock • Only inheritable traits can be passed down • Importance: Shows life can change over a period of time 2 4/2/2017 Dog traits have been selected by breeders for centuries to produce various breeds. Plants have been bred to produce certain traits for human use also! The Myth These kittens have variations What is the beaver comic showing? • Individuals don’t grow something because they need it. • Individuals don’t evolve. Populations evolve!!! Not all these wildebeest will survive •Four factors: 1) Overpopulation: more offspring are born than can survive 2) Variation: individuals of a population have differences 3) Adaptation: Some variations allow a better chance of survival 4) Descent w/ modification: Over time, those with advantages makeup more of the population Struggle for Survival •High birth rates and limited resources cause competition •Fitness: measure of the ability to survive & produce more offspring; fitness is a result of adaptation •Adaptations can be physical, behavioral, or temporal The Truth - Natural selection can act only on traits that currently exist. Adaptation Defined: An inherited trait that increases a population’s chances of survival and reproduction in a particular environment 3 4/2/2017 Adaptations Structural Adaptations Mimicry Behavioral Adaptation Temporal Adaptation Some cicadas reproduce every 13 years while others reproduce every 17 years, so the two groups never cross paths and reproduce. Blue-footed boobies have a courtship display that is unique to their species; they will not mate until that courtship display is completed. Which rabbit is best adapted? What happens when environments change? Year 1 Background Do the dark rabbits turn white? No! They get eaten. Year 10 Background Those best adapted survive and reproduce. 4 4/2/2017 Changing Environments •As environments change… –Those with adaptation: more likely to survive & reproduce –Those without adaptation: more likely to perish Limited Resources Overproduction Variation Populations produce too many young; many must die Individuals show variation; some variations are more favorable than others •Populations do not grow unchecked Natural Selection Natural selection favors the best suited at the time –Limiting Factors: food, water, shelter, disease, predators Inheritance Variations are inherited. The best suited variants leave more offspring. Summary of Darwin’s Theory of Evolution by Natural Selection Over time, natural selection results in changes in inherited characteristics of a population. • Darwin’s principle states that over time, living species have descended, with changes, from other species. • This implies that all living organisms are related to one another. •Defined: Collection of every known fossil •Most fossils found in sedimentary rock •Age determined by depth –new rock forms on top of older rock •Evidence Conclusions: 1) Newer fossils are more complex 2) Common ancestors: relationships between ancient & modern life Fish evidence Reptile Evidence Whale Evidence Scales Teeth Long spine Amphibian Land Evidence evidence Bird Evidence Eyes on Wolf-like top of head teeth Wishbone Bony Fins Foundtail in dried up oceans Found in driedup oceans Wrist bones Hind legs Feathers • AKA: Transition Fossils –Archaeopteryx: shares both bird & reptile features –Basilosaurus: shares whale & land mammal features –Tiktaalik: shares fish & amphibian features • Evidence Conclusion : Indicates common ancestry 5 4/2/2017 •Different species show similar development patterns •Different body plans become noticeable later in development •Evidence Conclusion : Indicates common ancestry • Defined: similar body structures with very different functions • Different environments lead to adaptations – Ex: The forelimbs of animals • Evidence Conclusion : Indicates common ancestry •Defined: Organs which have lost most or all their original function •Vestigial Human Parts: • Defined: similar function with very different structures • Analogous structures are not evidence of a common ancestor. –Gill slits = once used to breath oxygen in water –Yolk sac = once used to nourish developing embryo –Tailbone = once used for balance –Appendix = once used to digest plants –Wisdom teeth = once used to grind plant tissue •Evidence Conclusion : Indicates common ancestry Human Embryo w/ Vestigial Structures Pythons have tiny femurs (leg bone) 6 4/2/2017 • DNA, RNA, proteins compared • Genetic code same for most life Ch. 16 Evolution of Populations •More related species have more similar biochemistry •Evidence Conclusion: Indicates common ancestry 16.1 Genes & Variation •Gene Pool: All alleles within a population •Relative Frequency: number of times that an allele occurs in a gene pool; usually expressed as a percent How Twitter is upgrading our gene pool… Allele Frequencies: Sum = 100% Frequency of black allele = 12/20 = 60% Frequency of white allele = 8/20 = 40% Does gene frequency equal phenotype frequency? Why or why not? White allele is recessive to black allele. No, because some black mice carry the recessive allele. Sources of Genetic Variation • Genetic variation can increase chances some survive changing environments • Two main causes of genetic variation: 1. Mutations: Random changes to DNA sequence affect phenotypes; may affect fitness (ability to survive and reproduce) 2. Gene Shuffling: During meiosis, genes recombine in varying patterns; does NOT change the relative frequencies of alleles! 7 4/2/2017 16.2 Evolution as Genetic Change Natural Selection acts on phenotypes, not genotypes • Happens over generations • Can lead to changes in allele frequency (Evolution!) Freq. of green allele: Individuals that are better suited to their environment (have high levels of fitness) survive & reproduce most successfully. Types of Selection Freq. of brown allele: Types of Selection Directional Selection— Individuals at one end of the curve have a higher fitness than the rest. Disruptive Selection— Individuals at the upper and lower ends of the curve have a higher fitness; Selection creates two distinct phenotypes. Types of Selection Stabilizing Selection— Individuals near the center of the curve have higher fitness. Genetic Drift • Defined: Changes in allele frequencies due to chance –NOT natural selection • Bottleneck effect –Results in a loss of genetic variation (alleles) –More likely in smaller populations –Example: Natural disaster •Pre-forest fire: Green is best adapted (blend better) •Post-forest fire: Brown more likely to reproduce –Survival UNRELATED to adaptations 8 4/2/2017 Genetic Drift: Founder Effect • Situation in which allele frequencies change as a result of the migration of a small subgroup of a population. • Example: Hawaiian fruit flies descended from 1 main type—very different from mainland fruit flies Speciation Defined: evolution of new species from an existing species • 5 factors that lead to evolution Natural Selection Gene flow Mutations Sexual selection Genetic drift Reproductive Isolation • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species 1) Geographic Isolation: o Organisms isolated by geographic barrier Random DNA mutations Random DNA mutations Different predators Different predators Different resources Different resources 16-3 The Process of Speciation Species •Defined: group of organisms that can interbreed and produce fertile offspring –Different species rarely breed –Interspecies breeding often results in sterile offspring •Ex: Horse x Donkey = Mule •Ex: Lion x Tiger = Liger –New species = when unable to successfully reproduce Gene Flow (Migration) •Defined: Movement of alleles from one population to another - Increases variations in a population - Keeps differing populations similar •If gene flow is prevented - No variations (alleles) exchanged - Populations are isolated - Organisms adapt to their own environment - Can lead to speciation! 9 4/2/2017 Reproductive Isolation Reproductive Isolation • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species 1) Geographic Isolation: o Organisms isolated by geographic barrier 2) Behavioral Isolation o Organisms isolated by differing mating rituals Current Evolution: If the mating calls do not attract each other, will they reproduce? Is gene flow stopped? • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species 1) Geographic Isolation: If one group mates during the spring… o Organisms isolated by geographic Is gene flow stopped? barrier And the other mates during the fall… 2) Behavioral Isolation o Organisms isolated by differing mating rituals 3) Temporal Isolation o Organisms isolated by differing times of reproduction •Constant creation of chemicals for human use is eliminating the “unfit” organisms –Ex: Antibiotics eliminating unfit bacteria •Constant creation of chemicals for human use is eliminating the “unfit” organisms When The antibiotics infected with are absorbed a bacteria,into we the take antibiotics. bacteria. –Ex: Antibiotics eliminating unfit bacteria Bacteria A is more likely to survive and _________________. REPRODUCE antibiotic antibiotic Alexander Fleming discovered the first antibiotic… penicillin antibiotic antibiotic Bacteria A Bacteria B antibiotic antibiotic Bacteria A antibiotic Bacteria A has genes to create enzymes that destroy the antibiotic antibiotic Bacteria B does not have the genes to make the enzymes to destroy the antibiotic •Constant creation of chemicals for human use is eliminating the “unfit” organisms –Ex: Antibiotics eliminating unfit bacteria –Ex: Pesticides eliminating unfit pests 10 4/2/2017 •Constant creation of chemicals for human use is eliminating the “unfit” organisms –Ex: Antibiotics eliminating unfit bacteria –Ex: Pesticides eliminating unfit pests •Constant creation of chemicals for human use is eliminating the “unfit” organisms Some “pests” are able to resist the pesticides and survive. They will reproduce with others who are resistant. Over time, the entire population is resistant. –Ex: Antibiotics eliminating unfit bacteria –Ex: Pesticides eliminating unfit pests Pesticides pesticides pesticides pesticides pesticides pesticides •Constant creation of chemicals for human use is eliminating the “unfit” organisms –Ex: Antibiotics eliminating unfit bacteria –Ex: Pesticides eliminating unfit pests –Ex: Antivirals… –Ex: Fungicides… •This is natural selection! –Allows resistant to survive and reproduce Read before the video, answer after….. 1. Why is the Russian prison system considered to be "ground zero" in the fight against TB? 2. What is responsible for the evolution of TB strains that are resistant to multiple drugs? 3. How does the misuse of antibiotics affect the evolution of disease-causing bacteria? Use the theory of natural selection to explain the growing resistance to antibiotics. 4. Why should we care about a resistant strain of TB in Russia? Why Does Evolution Matter Now? 11