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Transcript
Evolution: Evidence of Change Welcome Back after spring Break Agenda Classroom guidelines Review for test Completion of missing work Classroom Guidelines You are welcome to seek clarifications Be responsible and follow good etiquette 5 minutes to settle when the class starts ( this includes washroom break, water etc.) Read activity instructions always in your handout. Raise your hand if you have any questions or if you need help No cellphone usage while I am teaching and when you are given a task to do No washroom break while I am teaching unless it is an emergency Bring textbook to class, no going back to locker Submit your activity sheets on the same day 5 minutes before you leave the class. If you need more time to complete the task, ask me Homework due next class Evolutionary relationship Evolution Evolution is the process of change in species driven by the selective pressure of natural agents Video on Darwin and evidences of evolution https://www.youtube.com/watch?v=XKnqj3YFXU8 Darwin’s work and original manuscripts (additional info if you are interested) http://darwin-online.org.uk/majorworks.html http://www.bbc.co.uk/timelines/zq8gcdm#zxq987h Evidence for evolution! Charles Darwin contributed enormously to our understanding of the process of evolution At the age of 22, Charles Darwin (1809-1882) climbed aboard the H.M.S. Beagle, to sail the world for 5 years Carolus Linnaeus (1707-1778) Developed modern classification system Grouped organisms into taxa Taxa: Group of one or more populations that form a unit based on similar characteristics (relatedness) of Organisms Physical similarities, observable characteristics Hinted at the idea of common ancestors Developed Binomial Nomenclature The two name naming system that remains in use today Jean Baptiste de Lamarck (1744-1829) Brought the idea of evolution to the forefront He realized that organisms adapted to their environments Lamarck’s theory is based on 3 ideas: Desire (the will) to change Use and Disuse Passing on acquired traits Knew nothing of genes or genetics, didn’t understand the how He’s known most famously for the giraffe neck stretch hypothesis Darwin’s Other Influences contd. Alfred Russel Wallace Focused on Biogeography of animals. Wrote a book ”The geographic distribution of animals” Developed the theory “evolution by natural selection” independently at same time as Darwin (1858--) Both Darwin and Wallace presented their work at Linnaean Society and Wallace insisted that Darwin should receive the credit Darwin’s Theory of Natural Selection- Five reasons of Evolution 1. Overproduction Ex. Millions of eggs laid annually by cod fish Populations increase geometrically while food resources multiply arithmetically 2. Struggle for existence (competition) Food, water and space 3. Variation Differences in traits among members of same species Variation is inherited 4. Survival of the fittest (natural selection) Fitness is not always about strength; it includes any characteristic that increases an organism’s chances of survival and reproduction Fitness arises from a process called adaptation, which is environmental selection of advantageous characteristics 5. Origin of new species or the principle of common descent New organism come from preexisting organisms; thus, each species has descended from the offspring of other species over time Direct evidences of Evolution: Galapagos finches – Variation in beak Direct Evidence for Evolution Fossils Preserved remains or traces of an organism that lived in the past. Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock. Direct evidence: Environmental selection – adaptation - The Peppered Moth Spend their time resting on tree trunks. Some are born light coloured; some are dark Can you see them both? Which one is easier to spot? The Industrial revolution in England deposited large quantities of soot from factories, staining the trees. Now which is easier to spot? Lamarck vs. Darwin Lamarck Environment causes giraffes to stretch their necks over their lifetime to better survive. Darwin Environment selected that giraffes born with longer necks had a greater chance of survival Indirect Evidence for Evolution Homologous Structures Modified body parts with different functions that developed from the same ancestral parts Embryological Relationships Structural similarities between species during embryonic development i.e. Gill slits in humans Indirect Evidence for Evolution Vestigial Structures Structures in the body of organisms that seem to serve no useful purpose at all May have had a function in ancestral forms Eg. human tailbones, the appendix Muscles that move our ears Whale hip bones Indirect Evidence for Evolution Comparative biochemistry and molecular evidence All organisms have similarities in their biochemistry Cytochrome c, Hemoglobin etc. ATP, Carbon The more closely two species are related, the closer the similarities between their genes All life has DNA, Humans share: 98% of our genes with chimpanzees; 65% with chickens; 60% with bananas; 7% with bacteria Biochemical Relationship- Hemoglobin Role of DNA in Evolution-We are related to other species 98% of our genes with chimpanzees; 65% with chickens; 60% with bananas; 7% with bacteria 20 Discovery of DNA Structure Rosalind Franklin took diffraction x-ray photographs of DNA crystals In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays copyright cmassengale 21 DNA Structure • Two strands coiled hence called a double helix • Sides made of a pentose sugar Deoxyribose, bonded to phosphate (PO4) groups by phosphodiester bonds • Center made of nitrogen bases bonded together by weak hydrogen bonds copyright cmassengale 22 DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone copyright cmassengale 23 DNA • Stands for Deoxyribonucleic acid • Made up of subunits called nucleotides • Nucleotide made of: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base copyright cmassengale 24 DNA Nucleotide Phosphate Group O O=P-O O 5 CH2 O N C1 C4 Sugar (deoxyribose) copyright cmassengale C3 C2 Nitrogenous base (A, G, C, or T) DNA 25 5 O 3 3 P 5 O O C G 1 P 5 3 2 4 4 P 5 P 2 3 1 O T A 3 O 3 5 O copyright cmassengale 5 P P 26 Antiparallel Strands One strand of DNA goes from 5’ to 3’ (sugars) The other strand is opposite in direction going 3’ to 5’ (sugars) copyright cmassengale 27 Nitrogenous Bases • Double ring PURINES Adenine (A) Guanine (G) A or G • Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C copyright cmassengale 28 Base-Pairings Purines only pair with Pyrimidines Three hydrogen bonds required to bond Guanine & Cytosine 3 H-bonds G copyright cmassengale C 29 •Two hydrogen bonds are required to bond Adenine & Thymine T copyright cmassengale A 30 Discovery of DNA Structure Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G) In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9% copyright cmassengale 31 Question: • If there is 30% Adenine, how much Cytosine is present? copyright cmassengale 32 Answer: • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C-G copyright cmassengale DNA double helix Chemistry Genes: Unit of Variation Darwin’s variation can be best expressed using the experiments of Gregor Mendel (1822-1884). Mid 19th century, biologists believed that inheritance was blended traits of offspring were the average of their parents. Blended inheritance was discredited by Gregor Mendel’s experiments, which showed that inheritance was particulate. He began our understanding of genetics. Mendel’s Experiment 1. Experimented with Pea Plant breeding. 2. Focused on 7 well-defined garden pea traits one at a time: • • Flower/seed coat color: purple vs. white flowers grey vs. white seed coats Seed color: yellow vs. green • • • • • Seed shape: smooth vs. wrinkled Pod color: green vs. yellow Pod shape: inflated vs. pinched Stem height: tall vs. short Flower position: axial vs. terminal Genotype = collection of genes (and alleles) in an organism Phenotype = observable properties of an organism Mendel’s Theories The genes for different traits are inherited independently of each other. Some exceptions, of course, occur Incomplete Dominance (blending) for some traits Codominance (random mixing) Some genes are sex-linked Seed shape Seed color Pod shape Mendel’s 7 garden pea characters. Pod color Flower color Flower location Plant size Monohybrid Cross When he bred a purebred tall plant with a purebred short plant, all off the offspring were tall Then, when he bred two plants of the new generation together, he would get 1 short plant for every 3 tall plants. Purebred tall × Purebred short F1 generation = all tall F1 × F1 F2 generation = 3 tall : 1 short Monohybrid Cross - explained Parental generation TT tt × F1 = all Tt F1generation This is called a Punnett’s Square Tt Tt × T t T TT Tt t Tt tt F2 phenotypic ratio = 3:1; genotypic ratio = 1:2:1 Dihybrid Cross Pgeneration Purebred tall ; Green pods × Purebred short; yellow pods F1 = all tall; green pods F1 × F1 F2 = 9 tall/green : 3 tall/yellow : 3 short/green : 1 short/yellow The 5 Agents of Evolutionary Change Natural Selection Environmental selection of advantageous traits Mutation Random changes in protein structure (See DNA presentation) Genetic Drift Gene Flow Non-Random Mating So, how does Selection work on genes? Population A group of organisms of the same species and living in the same area Therefore, sharing the same gene pool Evolution works on populations not on individual organisms Variation occurs in individuals Selection shifts the relative frequency and abundance of alleles in a gene pool The Genetic definition of evolution: Any change in the relative frequency of alleles in the gene pool of a population. Types of Selection Directional One extreme form of a trait is favoured Stabilizing Intermediate form of a trait is favoured Disruptive Both extreme forms of a trait are favoured Genetic Drift Random process that increases the specific allele frequency within a population Reduces variation within a population, which can result in a lack of diversity Promoted allele may not be advantageous Occurs most often in smaller populations Often due to a disaster or disease event Surviving individuals have different allele frequencies than the original population Reproductive Isolation Reproductive Isolation Darwin’s Finches Spatial (geographic) isolation of Finches in the Galapagos resulted in their evolution into different species. Gene Flow (Migration) Gene flow—also called migration—is any movement of genes from one population to another. Ex: pollen being blown to a new destination or people moving to new cities or countries. Can be very important source of genetic variation Non-random Mating Non-random mating some organisms are more desirable mates than others. organisms with this desirable trait are more likely to mate and produce offspring with similar characteristics Desirable trait may not improve fitness The Patterns of Evolution Divergent Evolution Reproductive Isolation often results in Divergent evolution The process by which one species gives rise to two or more new species, whose traits become more and more different, but who share a common, structural ancestor Produces homologous structures Different function, but same origin Convergent Evolution The process by which two or more different species evolve to become structurally similar Species must have similar niches Ex. shark and dolphin Produces analogous structures Similar function, but different origin Parallel Evolution The process where two different species follow similar evolutionary paths Species must have similar niches Ex. Timber wolf and Tasmanian wolf Sleek, hunters, etc… Co-evolution When two or more species influence each other's evolution. It is most often invoked to explain coadaptations between species. Ex: Parasites and Hosts (antagonistic coevolution) can lead to evolutionary 'arms races‘ Ex: Insects and Flowering Plants (mutualistic coevolution) The Tempo of Evolutionary Change Gradualism Theory that evolutionary change occurs slowly and gradually true for many species in fossil record Punctuated Equilibrium Term used to describe a pattern of long stable periods interrupted by brief periods of change. Living Fossils Some organisms have changed very little over the past million years E.g. Ginko biloba (270 MYA) Hagfish (300 MYA) Red Panda (10 MYA) Pelicans (30 MYA) Crocodiles (83.5 MYA) Evolutionary Change Rapid Change Sometimes something happens to upset the equilibrium and change happens rapidly Ex: bottleneck, or a small group of organisms migrates to new environment MASS EXTINCTION – many species vanished due to global climate changes When many species die it leaves TONS of niches unoccupied!! Historical Mass Extinctions Suddenly, Bobby felt very alone in the world