II HardyWeinberg Principle Predicts allele frequency in a

II. Hardy-Weinberg Principle • Predicts allele frequency in a non-evolving population; that is, a population in equilibrium States that allele frequencies in a population will remain constant from generation to generation if five conditions are met • Used to identify evolving/study populations

II. Hardy-Weinberg Principle, cont • Five Conditions for Hardy-Weinberg Equilibrium: 1. 2. 3. 4. 5. No natural selection No mutations Large population No migration Random mating • If any of these conditions are not met, …

IV. MICROEVOLUTION • A change in the gene pool of a population over a succession of generations • Five main causes: Ø mutation Ø non-random mating Ø gene flow Ø genetic drift Ø natural selection

IV. MICROEVOLUTION, cont • Mutations • Ultimate source of variation • random • Alone cannot cause adaptive change • Must precede selective event for adaptation to occur

V. VARIATION IN POPULATIONS • Genetic Variation o Critical for species/population success o “Fodder” or “Substrate” for evolution ØMutation: The ULTIMATE source of variation Ø Sex and Diploidy: independent assortment, random fertilization, and heterozygous genotypes

IV. MICROEVOLUTION, cont • Genetic Drift o. Changes in the gene pool due to chance. o. More often seen in small population sizes. (sampling error greater in smaller populations) o. Usually reduces genetic variability. o. There are two situations that can drastically reduce population size: ØBottleneck Effect Øindiscriminate large-scale loss ØFounder Effect ØColonization by a few

IV. MICROEVOLUTION, cont • Bottleneck Effect v. Type of genetic drift resulting from a reduction in population (natural disaster) v. Surviving population is no longer genetically representative of the original population

IV. MICROEVOLUTION, cont • Founder Effect v. Due to colonization by a limited number of individuals from a parent population v. Gene pool is different than source population

Whatever the type, genetic drift causes the loss of diversity/variation in a population. • Some alleles will be lost from the gene pool • Some will take over— become fixed

IV. MICROEVOLUTION, cont • Gene Flow ØGenetic exchange due to the migration of fertile individuals or gametes between populations ØTends to reduce differences between populations ØMust be stopped for speciation to occur

IV. MICROEVOLUTION, cont • Nonrandom Mating ØInbreeding ØMate with relatives ØMate by proximity ØAssortative mating ØMate with those having similar characteristics ØOther kinds of Sexual selection Ø“Gee, those eyebrows are lovely”

IV. MICROEVOLUTION, cont • Natural Selection 1. Variation of heritable traits exists in a population (Mutation/variation precedes selection!) 2. Environment changes 3. Alleles/traits imparting more relative fitness tend to be passed on to offspring more frequently 4. accumulation of favorable alleles/traits results— change in gene pool ØOnly form of microevolution that adapts a population to its environment

VI. A CLOSER LOOK AT NATURAL SELECTION • Natural Selection v. Not a random process → Dynamic process v. Increases frequency of alleles that provide reproductive advantage ØFitness v. Natural selection is the only evolutionary mechanism for adaptive evolution

VI. CLOSER LOOK AT NATURAL SELECTION, cont • Three common ways in which natural selection may alter variation v. Directional v. Disruptive v. Stabilizing

VI. CLOSER LOOK AT NATURAL SELECTION, cont • Balanced polymorphisms • Natural selection maintains more than one allele in a gene pool for certain genes 1. Heterozygote advantage • • • Imparts more fitness than either homozygous genotype Sickle cell-disease Book: “Survival of the sickest” 2. Frequency-dependent selection • Rarer genotypes/alleles have an advantage over more common ones

VI. CLOSER LOOK AT NATURAL SELECTION, cont • Sexual Selection ØCan result in sexual dimorphism secondary sex characteristic distinction ØIntrasexual Selection ØMale vs male competition (real and ritualized) ØIntersexual Selection ØOmg, I love his plumage/throat bag/etc. !

VII. MACROEVOLUTION • Macroevolution ØRefers to the formation of new taxonomic groups ØDue to an accumulation of microevolutionary changes ØAKA Speciation • “Species” ØBiological Species Concept ØTwo organisms are from the same species if they can… ØInterbreed, producing fertile offspring

VII. MACROEVOLUTION Reproduction • Asexual vs Sexual Reproduction • Asexual advantages: • All mutations passed to all offspring • Lower commitment of resources for reproduction • Usually faster • Asexual Disadvantages • Unless there is recombination via horizontal gene flow, multiple advantageous mutations must happen in same line for continued adaptation

VII. MACROEVOLUTION Reproduction • Asexual vs Sexual Reproduction • Sexual advantages: • Beneficial mutations can originate in different individuals and end up in the same individuals through sexual recombination—accelerates evolutionary changes • Sexual Disadvantages • High commitment of resources (competition, energy, time) • High failure rate, must find mate • Usually in animals that reproduce more slowly.

Having your cake and eating it too…doing it both ways.

VII. MACROEVOLUTION, cont • Reproductive Isolation o Important to maintain integrity & continuity of a species o Prevents closely related species from interbreeding when their ranges overlap. o Divided into 2 types ØPrezygotic ØPostzygotic

VII. MACROEVOLUTION, cont

VII. MACROEVOLUTION, cont

VII. MACROEVOLUTION, cont • Speciation o Fossil record shows evidence of bursts of many new species, followed by periods of little chance ØKnown as punctuated equilibrium, proposed by Gould o Other species appear to change more gradually ØGradualism fits model of evolution proposed by Darwin

VII. MACROEVOLUTION, cont • Modes of Speciation ØBased on how gene flow is interrupted

VII. MACROEVOLUTION, cont ØAllopatric § Populations segregated by a geographical barrier; can result in adaptive radiation (island species)

VII. MACROEVOLUTION, cont ØSympatric § Reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

IX. PHYLOGENY

IX. PHYLOGENY, cont • Taxonomy ØNaming and classifying of organisms ØBinomial nomenclature ØMolded by phylogeny

IX. PHYLOGENY, cont • Node • Clade • Monophyletic group • Sister taxa • Basal taxon • Outgroup • Root • Paraphyletic • Polyphyletic

IX. PHYLOGENY, cont § Taxa are sub-categorized as Ø Monophyletic – Includes ancestral group and all descendants v Clade Ø Paraphyletic – Includes ancestral group and some, but not all descendants Ø Polyphyletic – Includes taxa with multiple ancestors

IX. PHYLOGENY, cont • Tree Construction ØHomology § Heritable traits shared by 2 or more ancestors § Example: backbone in all vertebrates § Important to distinguish between homologies and analogies v Homologies are likenesses attributed to common ancestry v Analogies are likenesses attributed to similar ecological roles and natural selection v Analogies are also known as homoplasies § May also be done at a molecular level

IX. PHYLOGENY, cont • Tree Construction, cont ØAncestral Trait ØDerived Traits § Evolutionary novelties, “new” adaptations § May see evolutionary reversals § Relative term § Shared derived traits defines groups ØIngroup § Groups of organisms being considered, phylogenetically organized ØOutgroup § Group chosen as point of reference for tree § Closely related but diverged before the ingroups

IX. PHYLOGENY, cont • Tree Construction, cont ØParsimony § Also known as Occam’s Razor § Principle that if multiple trees are possible, the correct one is most often the one with the fewest evolutionary changes

Other Molecular Phylogeny Methods

IX. PHYLOGENY, cont Ring of Life

IX. PHYLOGENY, cont • Phylo. Code

VIII. HISTORY OF LIFE ON EARTH

VIII. HISTORY OF LIFE ON EARTH, cont • Formation of Organic Molecules o. Oparin/Haldane Hypothesis Ø Primitive Earth’s atmosphere was a reducing environment Ø No O 2 Ø Early oceans were an organic “soup” Ø Lightning & UV radiation provided energy for complex organic molecule formation

VIII. HISTORY OF LIFE ON EARTH, cont • Formation of Organic Molecules, cont o. Miller/Urey Experiment ØTested Oparin/Haldane hypothesis ØSimulated atmosphere composed of water, hydrogen, methane, ammonia ØAll 20 amino acids, nitrogen bases, ATP formed ØHypothesis was supported

RNA World Hypothesis • Ribozymes • Ribosomes • Self-replicating RNA • RNA can be used as a template and act as a catalyst

VIII. HISTORY OF LIFE ON EARTH, cont Caused by cyanobacteria releasing O 2

VIII. HISTORY OF LIFE ON EARTH, cont

VIII. HISTORY OF LIFE ON EARTH, cont • Mass Extinctions Permian Extinction K-T extinction

VIII. 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

Convergent and divergent evolution