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Transcript
UNIT VIII EVOLUTION • Big Campbell Ch 22-28, 31 • Baby Campbell Ch 13-17 • Hillis Ch 15-18 I. EVOLUTION - WHAT IS IT? o “Descent with Modification” Earth’s many species are descendants of ancestral species that were diff. than present day species o Evolution – change in the genetic composition of a population over time. “Change” – in the genetic composition (the alleles) Population – group of organisms of one species in a certain habitat that interbreed to produce fertile offspring. November 24, 1859 II. Hardy-Weinberg Principle • Predicts allele frequency in a non-evolving population; that is, a population in equilibrium o States that allele frequencies in a population will remain constant from generation to generation if five conditions are met o Used to identify/study evolving populations II. Hardy-Weinberg Principle, cont • Five Conditions for Hardy-Weinberg Equilibrium: 1) No Mutations – gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated 2) Random Mating – if individuals mate preferentially within a population (inbreeding), random mixing of gametes does not occur and gene frequency changes. 3) No natural Selection – differences in the survival and reproductive success of individuals carry diff. genotypes and can alter allele frequencies. 4) Extremely large population size – the smaller the pop the more likely allele frequencies will fluctuate by chance from one generation to the next (genetic drift) 5) No gene flow (migration) – moving alleles into or out of populations can alter allele frequencies. If any of these conditions are not met, evolutionary change will occur! II. Hardy-Weinberg Principle, cont • Hardy-Weinberg Equation p = frequency of one allele (A) q = frequency of other allele (a) p + q = 1 (sum of 2 alleles = 1 or 100%) • Therefore, p=1-q q=1-p • Genotype Frequency AA = p2 aa = q2 Aa = 2pq • To determine distribution of genotype frequencies in a population → p2 + 2pq + q2 = 1 Ex: PKU in the US • • • • • • Autosomal Recessive Occurs 1 in 10,000 births q2 = .0001 q = .01 p = 1 - .01 = .99 What % of individuals are carriers for PKU? • 2pq = 2(.99)(.01) = .0198 or 2% II. Hardy-Weinberg Principle, cont Hardy-Weinberg Practice Problems 1. If you know that you have 16% recessive fish (bb), . . . • q2= • q= • Therefore, p = To calculate the frequency of each genotype … • p2 = • 2pq = What is the expected percentage of heterozygous fish? II. Hardy-Weinberg Principle, cont • Hardy-Weinberg Practice Problems, cont 2. If in a population of 1,000, 90 show recessive phenotype (aa), use HardyWeinberg to determine frequency of allele combinations. 3. In people light eyes are recessive to dark. In a population of 100 people, 36 have light eyes. What percentage of the population would be … • Homozygous recessive? • Homozygous dominant? • Heterozygous? II. Hardy-Weinberg Principle, cont 4. The ability to roll the tongue is a dominant trait. … 75% of the students at Kingwood Park High School have the ability to roll the tongue. Assuming the student population is 1700, a) How many students would exhibit each of the possible genotypes? b) How many students would exhibit each of the possible phenotypes? III. A HISTORY OF EVOLUTIONARY THEORY • Aristotle (384-322 BCE) o Scala Naturae • Carolus Linnaeus (1707-1778) o Taxonomy III. A HISTORY OF EVOLUTIONARY THEORY, cont III. A HISTORY OF EVOLUTIONARY THEORY, cont • Charles Darwin (1809-1882) III. A HISTORY OF EVOLUTIONARY THEORY, cont • Darwin, cont o Observed many examples of adaptations Inherited characteristics that enhance organisms’ survival and reproduction o Based on principles of natural selection Populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others Differential reproductive success III. A HISTORY OF EVOLUTIONARY THEORY, cont • Darwin’s Conclusions Based on his own observations and the work of other scientists, Darwin realized … o Members of a population often vary greatly in their traits. o Traits are inherited from parents to offspring. o All species are capable of producing more offspring that their environment can support, therefore … III. A HISTORY OF EVOLUTIONARY THEORY, cont Darwin concluded … o Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals. o This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations. Descent with Modification III. A HISTORY OF EVOLUTIONARY THEORY, cont Human Directed Evolution? • Artificial Selection – Selective Breeding – Transgenic Organisms III. A HISTORY OF EVOLUTIONARY THEORY, cont • Post-Darwin Neo-Darwinism/Modern Synthesis Theory Epigenetics IV. EVIDENCE FOR EVOLUTION • Direct Observation o Antibiotic/Drug Resistance IV. EVIDENCE FOR EVOLUTION, cont • Fossil Record o Succession of forms over time o Transitional Links o Vertebrate descent IV. EVIDENCE FOR EVOLUTION, cont • Homology o Homologous structures o Vestigial organs Snakes Cetaceans Flightless birds IV. EVIDENCE FOR EVOLUTION, cont o Convergent Evolution Independent evolution of similar features in different lineages Analogous structures IV. EVIDENCE FOR EVOLUTION, cont • Biogeography o Geographical distribution of species o Continental Drift Pangaea o Endemic species o Islands are inhabited by organisms most closely resembling nearest land mass IV. EVIDENCE FOR EVOLUTION, cont • Comparative Embryology o Pharyngeal Pouches Gill slits o Tail IV. EVIDENCE FOR EVOLUTION, cont • Molecular Biology o Similarities in DNA, proteins, genes, and gene products o Common genetic code V. MICROEVOLUTION • A change in the gene pool of a population over a succession of generations • Five main causes: Mutation Non-Random Mating Natural Selection Genetic Drift Gene Flow V. MICROEVOLUTION, cont • Genetic Drift o o o o Changes in the gene pool due to chance. More often seen in small population sizes. Usually reduces genetic variability. There are two situations that can drastically reduce population size: Bottleneck Effect Founder Effect V. MICROEVOLUTION, cont • Bottleneck Effect Type of genetic drift resulting from a reduction in population (natural disaster) Surviving population is no longer genetically representative of the original population • Founder Effect Due to colonization by a limited number of individuals from a parent population Gene pool is different than source population V. MICROEVOLUTION, cont • Gene Flow Genetic exchange due to the migration of fertile individuals or gametes between populations – tends to reduce differences between populations V. MICROEVOLUTION, cont • Mutations A change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection) V. MICROEVOLUTION, cont • Nonrandom Mating Inbreeding – reduces fitness by putting an individual at a greater risk of harmful recessive traits. Assortative mating – individuals with similar genotypes/phenotypes mate more frequently than expected V. MICROEVOLUTION, cont • Natural Selection Blend of Chance and Sorting chance in the creation of new genetic variations; sorting b/c natural selection favors some alleles over others Relative fitness – contribution an individual makes to the gene pool of the next generation Only form of microevolution that adapts a population to its environment VI. VARIATION IN POPULATIONS • Genetic Variation is the “substrate” for evolution • Maintained through … Polymorphism Coexistence of 2 or more distinct forms of individuals (morphs) within the same population Geographical Variation Differences in genetic structure between populations (cline) VI. VARIATION, cont Mutation and Recombination Diploidy 2nd set of chromosomes hides variation in the heterozygote Balanced Polymorphism Heterozygote Advantage Frequency-Dependent Selection o Survival & reproduction of any 1 morph declines if it becomes too common o Parasite/host VII. A CLOSER LOOK AT NATURAL SELECTION • Natural Selection Not a random process → Dynamic process Increases frequency of alleles that provide reproductive advantage Fitness VII. CLOSER LOOK AT NATURAL SELECTION, cont Natural selection is the only evolutionary mechanism for adaptive evolution VII. CLOSER LOOK AT NATURAL SELECTION, cont • Three ways in which natural selection alters variation Directional Disruptive Stabilizing VII. CLOSER LOOK AT NATURAL SELECTION, cont • Sexual Selection Can result in sexual dimorphism - secondary sex characteristic distinction Intrasexual Selection - within the same sex; individuals of one sex compete directly for mates of the opposite sex Intersexual Selection - individuals of one sex are choosy in selecting their mate (male showiness) VIII. MACROEVOLUTION • Macroevolution Refers to the formation of new taxonomic groups Due to an accumulation of microevolutionary changes AKA Speciation • “Species” Morphological Species Concept - charac. species by body shape & other features; can be applied to sexual & asexual organisms Ecological Species Concept – views a species in terms of its niche; which is the sum of how members interact w/living & non-living parts of environ; can accommodate sex & asexual Phylogenetic Species Concept – smallest group of individuals that share a common ancestor; forming 1 branch on tree of life VIII. MACROEVOLUTION, cont • Biological Species Concept Described by Ernst Mayr in 1942 A population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring; in other words, similar organisms that can make babies that can make babies Can be difficult to apply to certain organisms . . . VIII. MACROEVOLUTION, cont • Reproductive Isolation o Prevent closely related species from interbreeding when their ranges overlap. o Divided into 2 types Prezygotic Postzygotic VIII. MACROEVOLUTION, cont Prezygotic Reproductive Barriers VIII. MACROEVOLUTION, cont Postzygotic Reproductive Barriers VIII. MACROEVOLUTION, cont • Speciation o Fossil record shows evidence of bursts of many new species, followed by periods of little chance Known as punctuated equilibrium o Other species appear to change more gradually Gradualism fits model of evolution proposed by Darwin VIII. MACROEVOLUTION, cont • Modes of Speciation Based on how gene flow is interrupted Allopatric Populations segregated by a geographical barrier; can result in adaptive radiation (island species) Sympatric Reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes IX. HISTORY OF LIFE ON EARTH IX. HISTORY OF LIFE ON EARTH, cont • Formation of Organic Molecules o Oparin/Haldane Hypothesis Primitive Earth’s atmosphere was a reducing environment No O2 Early oceans were an organic “soup” Lightning & UV radiation provided energy for complex organic molecule formation o Miller/Urey Experiment Tested Oparin/Haldane hypothesis Simulated atmosphere composed of water, hydrogen, methane, ammonia All 20 amino acids, nitrogen bases, ATP formed Hypothesis was supported IX. HISTORY OF LIFE ON EARTH, cont IX. HISTORY OF LIFE ON EARTH, cont IX. HISTORY OF LIFE ON EARTH, cont • Mass Extinctions IX. HISTORY OF LIFE ON EARTH, cont • Adaptive Radiation o Periods of evolutionary change, increased speciation o Often due to increased ecological niches in communities o Also seen in organisms with major evolutionary innovations X. PHYLOGENY Phylogeny – study of how living things share common evolutionary history (relationships among organisms) - Constructed based on physical structures, behaviors, and biochemical attributes - Commonly used to depict evolutionary history of species, populations, and genes. X. PHYLOGENY • Taxonomy Carrolus Linnaeus Binomial nomenclature – 2 part naming system; genus and species Taxon (taxa) – which is any group of species that we designate with a name. EX: humans, primates, mammals KPCOFGS Domain is broadest; organisms not as closely related Species is most specific X. PHYLOGENY, cont • Phylogenetics Tracing of evolutionary relationships Illustrated with diagrams known as phylogenetic trees May portray all life, or a major evolutionary group such as insects or mammals. Common ancestor is called the “root” X. PHYLOGENY • Tree Terminology Root – common ancestor of all organisms in the tree. Node – or split when a single lineage divides into two; giving rise to new lineages Clade Any taxon that consists of all evolutionary descendants of a common ancestor Clades are sub-categorized as Monophyletic – Includes ancestral group and all descendants Paraphyletic – Includes ancestral group and some, but not all descendants Polyphyletic – Includes taxa with multiple ancestors Sister Clades – any 2 clades that are each other’s closest relatives Sister Species – two species that are each other’s closest relatives Monophyletic – “single tribe” Paraphyletic ancestral group and some, but not all descendants “beside the tribe” Paraphyletic Polyphyletic Includes taxa with multiple ancestors EX: Kingdom Protista Polytomy • Unresolved pattern of divergence • More than 2 descendant groups emerge • Evolutionary relationships are not clear X. PHYLOGENY, cont • Evolutionary history of an organism X. PHYLOGENY, cont • Important to distinguish between homologies and analogies Homologies are likenesses attributed to common ancestry Analogies are likenesses attributed to similar ecological roles and natural selection • May also be done at a molecular level Known as molecular systematics X. PHYLOGENY, cont • Tree Construction, cont Ancestral Trait – trait from which organisms evolve; found in common ancestor Derived Traits – new traits that evolved after ancestral trait Synapomorphies – shared among a group of organisms; viewed as evidence for common ancestry of group. EX: vertebral column of vertebrates May see evolutionary reversals – a character may revert from a derived state back to an ancestral state. EX: finstetrapodsfins in whales/dolphins Ingroup Groups of organisms being considered, phylogenetically organized Outgroup Group chosen as point of reference for tree Closely related but diverged before the ingroups X. PHYLOGENY, cont • Tree Construction, cont Parsimony Also known as Occam’s Razor Principle that if multiple trees are possible, the correct one is most often the simplest one; one that takes the fewest assumptions X. PHYLOGENY, cont X. PHYLOGENY, cont X. PHYLOGENY, cont