AP Bio Evolution

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

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CH.

22: DESCENT WITH MODIFICATION

 Darwin's theory of natural selection:

Ch. 23: EVOLUTION OF POPULATIONS

CH. 24 ORIGIN OF SPECIES

 Reproductive Barriers - Steps to speciation

CH. 25 HISTORY OF LIFE ON EARTH

 Four main steps

 Tetrapod: mammal, amphibian, reptile

 Hierarchical classification and morphology (analogy) doesn’t reflect evolutionary history.

 Phylogeny: evolutionary history of species

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