UNIT VIII EVOLUTION Big Campbell  Ch 22-28, 31 Baby Campbell  Ch Hillis  Ch 15-18

I. EVOLUTION - WHAT IS IT? o “Descent with Modification” o  “ Change”  Population November 24, 1859

II. Hardy-Weinberg Principle Means used to determine if a population is evolving Predicts allele frequency in a non- evolving population; that is, a population in equilibrium oStates that allele frequencies in a population will remain constant from generation to generation if five conditions are met

II. Hardy-Weinberg Principle, cont Five Conditions for Hardy-Weinberg Equilibrium : 1) 2) 3) 4) 5) 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 = Therefore,  p =  q = Genotype Frequency  AA =  aa =  Aa = To determine distribution of genotype frequencies in a population →

II. Hardy-Weinberg Principle, cont Hardy-Weinberg Practice Problems 1.If you know that you have 16% recessive fish ( bb ),... q 2 = q = Therefore, p =  To calculate the frequency of each genotype … p 2 = 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 Hardy- Weinberg 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 High School have the ability to roll the tongue. Assuming the student population is 2526, 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 ( BCE) oScala Naturae Carolus Linnaeus ( ) o Taxonomy

III. A HISTORY OF EVOLUTIONARY THEORY, cont

Charles Darwin ( )

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 Artificial Selection

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: 

V. MICROEVOLUTION, cont Genetic Drift o Changes in the gene pool due to chance. o More often seen in small population sizes. o Usually reduces genetic variability. o 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  Assortative mating

V. MICROEVOLUTION, cont Natural Selection   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  Intersexual Selection

VIII. MACROEVOLUTION Macroevolution  Refers to the formation of new taxonomic groups  Due to an accumulation of microevolutionary changes  AKA Speciation “ Species”  Morphological Species Concept  Ecological Species Concept  Phylogenetic Species Concept

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 O 2  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

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 

IX. HISTORY OF LIFE ON EARTH, cont

X. PHYLOGENY Taxonomy  Linnaeus  Binomial nomenclature  Taxon (taxa)

X. PHYLOGENY, cont Evolutionary history of an organism

X. PHYLOGENY, cont Phylogenetics  Tracing of evolutionary relationships  Illustrated with diagrams known as phylogenetic trees

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 Cladistics  Use of common ancestry as primary criterion for classification  Species are put into groups known as clades  Includes ancestral species + descendents  Clades are sub-categorized as  Monophyletic – Includes ancestral group and all descendents  Paraphyletic – Includes ancestral group and some, but not all descendents  Polyphyletic – Includes taxa with multiple ancestors  Parsimony – Also known as Occam’s Razor

X. PHYLOGENY, cont