BIG IDEA #1
The process of
evolution
drives the
diversity and
unity of life.
MECHANISMS OF VARIATION
 Natural selection acts on phenotypic variations in populations
 Sources of variation:
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Mutation
Random assortment during meiosis
Crossing Over
Random Fertilization
Diploidy
 Allele Frequencies can be altered by:
 Gene Flow: Immigration and Emigration
 Genetic Drift: small populations
 Mating Patterns: Inbreeding and Sexual Selection
T YPES OF SELECTION
 Stabilizing Selection: favors intermediate phenotype
(heterozygote advantage)
 Directional Selection: favors one extreme over another
 Disruptive Selection: favors both extremes over the
intermediate
Campbell, Neil A. Reece; Jane B., BIOLOGY, 6th Edition 2002
PATTERNS OF EVOLUTION
 Convergent Evolution: two
dissimilar populations
evolve similar traits b/c of
similar selective
pressures. Ex: dolphin and
shark
 Parallel Evolution: similar
to convergent however,
organisms do not need to
occupy the same niches.
Ex: warning colors of
many organisms
 Divergent Evolution:
organisms from a common
ancestor become less
similar (adaptive
radiation) Ex: Galapagos
Tortois
EVIDENCE FOR EVOLUTION
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DNA
Amino acid sequence/similar proteins
Analogous structures
Vestigial structures
Homologous structures
CONDITIONS FOR HARDY-WEINBERG
EQUILIBRIUM
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Large population
Random mating
No mutations
No gene flow
No natural selection
DETERMINING ALLELE FREQUENCIES
 Frequency of dominant allele if frequency of recessive allele
is given
 p if q is given
 Frequency of recessive allele if the % of the population with
the recessive phenotype is given
 q if q 2 is given
 Calculate the % of the population with recessive allele if the
% of the population expressing the dominant allele is given
 q 2 if p 2 +2pq
SPECIATION
 Speciation occurs when
populations accumulate
enough changes over time
to lead to the emergence
of a new species.
 Types:
 Allopatric—geographic
barriers
 Sympatric—reproductive
barriers
 Polyploidy in plants leads to
new species b/c the
polyploids can not breed with
the diploid ancestors
MECHANISMS FOR REPRODUCTIVE
ISOLATION
 Prezygotic Isolating Mechanisms:
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Geographic (Habitat) Isolation
Ecological Isolation
Behavioral Isolation
Temporal Isolation
Mechanical Isolation
Sexual Isolation
 Postzygotic Isolating Mechanisms:
 Hybrid Sterility
 Hybrid Inviability
 Zygote Mortality
PRE AND POST ZYGOTIC MECHANISMS
FOR REPRODUCTIVE ISOLATION
ORIGINS OF LIFE
 Miller and Urey’s Experiment
 Amino acid monomers, polymers, protobiont, first cells
 Characteristics of the First Cells
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Unicellular
Heterotrophic
Prokaryotic
Simple lipid membrane
Ribosomes
RNA
 Autotrophic prokaryotes would appear soon after
ORIGINS OF COMPLEX CELLS
 Theory of Endosymbiosis —
Large eukaryotic cells
evolved when a small
prokaryotic cells was
engulfed by a larger
prokaryotic cell and they
developed a symbiotic
relationship where both
benefitted.
 Smaller one eventually
evolves into mitochondria (in
heterotrophs) or chloroplasts
(in autotrophs).
 Evidence: Mitochondria and
Chloroplasts have their own
DNA and ribosomes. They are
about the size of prokaryotes.
Their membranes are similar
to prokaryotes.
DIVERSIT Y OF LIFE
 Three Domains
 Bacteria
 Archae
 Eukarya
 Six Kingdoms
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Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
CLADOGRAMS
 Cladograms show relative relatedness between a group of
organisms