CH.
22: DESCENT WITH MODIFICATION
Darwin's theory of natural selection:
o Populations tend to over-reproduce
o Over reproduction leads to competition
o The best competitors are those with traits that are favorable in their environment. They
leave more offspring that survive and reproduce than others
o Advantageous traits accumulate over generation
Natural selection acts on traits that
o Affect survival and reproduction
o Vary genetically
o Heritable
Evidence for Natural Selection:
o Direct observations - drug-resistant bacteria
o Comparative anatomy - homology/analogy/vestigial structures
o Fossil record - past organisms differed from present, extinction, evolutionary changes, origin
of new populations
o Biogeography - influenced by adaptive radiation and continental drift
More recent common ancestor = more related
Definitions:
Principle of uniformitarianism: slow continuous change rather than sudden events; Earth is old
(Hutton and Lyell)
Linnaean system of classification: binomial nomenclature, 8 taxa, organisms based on evolution,
increasingly general categories
Differential reproductive success: favorable traits allow higher reproduction rate; these traits are
likely to appear frequently in the next generation
Homologous: variation is structures of similar species that was present in an common ancestor;
faced different environments (mammalian forelimbs, embryos)
o Divergent evolution: two species of a common ancestor evolve differently, with different
structures
Vestigial structures: remnants of a structure that once served a purpose in an ancestor
Analogous structures: similar structures in unrelated species; similar environments (bat and bird
wings)
o Convergent evolution: independent evolution of similar structures in different species
Ch. 23: EVOLUTION OF POPULATIONS
Microevolution caused by
o Natural selection, gene flow, and genetic drift
Only natural selection = adaptive evolution
Sources of Genetic Variation
o Mutations - low in prokaryotes, high in RNA, always slightly harmful
o New genes/Chromosomal changes - translocation, duplication, deletion, inversion
o Rapid reproduction - prokaryotes, RNA
o Sexual reproduction - crossing over, independent assortment of chromosomes, and
fertilization
Conditions for HW Equilibrium - only mendelian genetics
o No mutations - new alleles
o Random mating - genotypic frequencies change with sexual selection
o No natural selection - some alleles increase in frequency
o Large populations - small populations undergo genetic drift more often
o No gene flow - movement of alleles in/out populations alters allele frequencies
Modes of Natural Selection
o Directional
o Disruptive
o Stabilizing
o Sexual - results in sexual dimorphism
o Balancing
Frequency dependent
Heterozygote advantage
Why natural selection can't create perfect individuals
o Acts on existing traits/traits from ancestral anatomy
o Adaptations are compromises
o Environment can change
Definitions:
Microevolution: change in allele frequencies of a population over time; below species level
Gene variability: % of heterozygotes
Neutral variation: differences in DNA that don’t cause selective advantage or disadvantage (point
mutations, redundancy, ABO)
Gene pool: all copies of every allele at every locus in all members of population
H-W Equilibrium: allele and genotypic frequencies constant over generations
Adaptive evolution: traits that enhance survival and reproduction increase in frequency over time
Genetic drift: random events that cause unpredictable changes in allele frequencies (fertilization,
bottleneck effect, founder effect); new alleles can be fixed or alleles eliminated
o Founder effect: individuals isolated
o Bottleneck effect: something that reduces population size; alleles over/under-represented
Gene flow: reduces genetic variation b/t populations; maintains diversity within; prevents
speciation
Relative fitness: how much fertile offspring individual leaves compared to others
Sexual dimorphism: differences in 2ndary characteristics between males and females (size, color)
Frequency-dependent selection: less common phenotypes have selective advantage
Heterozygote advantage: preserve genetic variation in the form of recessive alleles
CH. 24 ORIGIN OF SPECIES
Reproductive Barriers - Steps to speciation
o Prezygotic - block fertilization; prevent mating attempt
Habitat Isolation
Temporal Isolation - seasonal differences
Behavioral Isolation - mate recognition
Mechanical Isolation - structural differences
Gamete Isolation - inability to fertilize
o Postzygotic - prevent a viable, fertile offspring
Reduced Hybrid Viability - reduced development
Reduced Hybrid Fertility - chromosomal differences
Hybrid Breakdown - 2nd generation hybrids sterile and feeble
Types of Speciation
o Allopatric - Geographic barriers
Mutations arise and natural selection and genetic drift alter allele frequencies,
keeping two populations separate
o Sympatric - Reproductive barriers that isolate subset of one population
Polyploidy
Sexual selection
Habitat differentiation
Hybrid Zones over time
o Reinforcement - prezygotic barriers strengthened; keeps two populations separate
o Fusion - single species; weak barriers
o Stability - better fitness than parent species
Patterns in fossil record
o Punctuated model: new species change the most as they branch out from parent species
and change little for the rest of their lives; rapid speciation
o Gradual model: gradual speciation; implies no missing links in fossil record
Definitions:
Biological species concept: species is a group of organisms that can produce viable, fertile
offspring by mating with only each other; slight gene flow
Reproductive isolation: barriers that block gene flow, interbreeding, and formation of hybrids
Polyploidy: extra sets of chromosome; common in plants
o Autopolyploid: extra set of chromosomes from same parent species
o Allopolyploid: extra sets of chromosomes in a hybrid
Hybrid zones: incomplete reproductive barriers; obstacle to gene flow
CH. 25 HISTORY OF LIFE ON EARTH
Four main steps
o Abiotic synthesis of organic molecules - first molecules were methane, ammonia, CO2, N,
water vapor, H
o Macromolecules - amino acid and RNA polymers
o Protocells - spontaneously form after organic molecules added to water
o Self-replicating molecules - based on RNA
Dating Fossils - favors species that existed for long time, abundant, and hard bones
First prokaryotes were anaerobic and heterotrophic; found in stromatolites
Cyanobacteria - oxygen revolution
Evidence supporting endosymbiosis
o Inner membrane same as bacteria
o Replication and protein synthesis similar to bacteria
o Similar ribosomes to bacteria
o Circular DNA
o Double membrane
o Grow and reproduce independently of cell
Rise and fall of groups of organisms detected by
o Plate tectonics - habitat, climate, speciation, distribution
o Mass extinctions - lead to adaptive radiation
o Adaptive radiation - due to vacant niches, major adaptations, little competition, climate
change
Complex structures evolve in increments of simpler steps that benefit owner but provide same
function
Single celled prokaryotes - oxygen rev. - single celled eukaryotes - multicellular eukaryotes -
Cambrian explosion - colonization of land
Definitions:
Tetrapod: mammal, amphibian, reptile
Endosymbiosis: anaerobic prokaryote cell engulfed bacteria (aerobic, archaea, heterotrophic) that
evolved into mitochondria. Then that cell engulfed a photosynthetic bacteria that evolved into
chloroplast.
Permian mass extinction: ocean life altered; extreme volcanos, global warming, ocean
acidification, oxygen levels decrease, anaerobic bacteria increase
Cretaceous mass extinction: wiped out dinosaurs
Differential species selection: species that reproduce the most and survive the longest determine
evolutionary trends
Exaptation: structures evolve for one function but used for another
Cambrian explosion: increase in diversity of life
CH. 26 PHYLOGENY
Hierarchical classification and morphology (analogy) doesn’t reflect evolutionary history.
Homology and molecular data does
Mitochondrial DNA evolves faster than rRNA, so used to compare recent relations
Gene duplication - mutations - natural selection - speciation - evolutionary change
Archaea more related to Eukarya than Bacteria
Traits that are shared by most species; proof of common ancestor:
o Vital body systems
o Fundamental cell processes
Ways to date fossils
o Relative dating - order of rock strata
o Radiometric dating - # of half-lives that passed
o Volcanic layers surrounding fossil
o Paleomagnetic dating - Earth's magnetic fields can shift and rotate
Definitions:
Phylogeny: evolutionary history of species
Systematics: process of classifying organisms by evolutionary history
Taxonomy: names of organisms (ex. Taxon = genus); uses Linnaean system
Cladistics: approach to systematics where organisms are placed into clades based on common
descent
Monophyletic group/taxon: groups of taxa that contains a common ancestor and all its
descendants (clade)
Paraphyletic group: common ancestor and some but not all descendants
Polyphyletic group: no recent common ancestor
Sister taxa: immediate common ancestor
Basal taxon: evolved early and unbranched
Polymorphism: existence of several different forms of a species in population (ABO)
Parallel evolution: two related species that have made similar adaptations after divergence
Coevolution: reciprocal set of adaptations
