AP Biology Exam Review
2002-2003
Heredity and Evolution – 25%
Evolutionary biology – 8%
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Early evolution of life
Evidence of evolution
Mechanisms of evolution
Related fields of study
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Paleontology: study of fossils
Comparative anatomy: study of structural
similarities among organisms
Comparative embryology: study of
embryological similarities among organisms
Taxonomy: study of organism groupings
with similar homologous structures (including
vestigial organs)
Biochemistry: chemical reactions in living
things
Terminology
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Population: localized group of individuals of
the same species
Species: group of population whose
individuals have the potential to interbreed
and produce fertile offspring
Gene pool: total aggregate of all genes in a
population at any given time
Tenets of evolution
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Natural selection “edits” the available gene
pool for a species.
Natural selection is contingent upon time and
place. Certain variations in a population
(group of species residing in one area) are
more favored for survival than others.
Mutations are a sources of variation in a
population.
“Descent with modification”
DDT &
Insects
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Insects with DDT
resistance also have
reduced metabolism.
Without DDT present,
these insects are not
adapted for the
environment.
Homology vs. Analogy
Three kinds of homologies –
having common origin
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1. Anatomical homology: example,
forelimbs
2. Embryological homology: example,
Eustachian tube in humans and all mammals
3. Molecular homology: DNA, RNA as
genetic code (shown through RFLP analysis)
Molecular
homology
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Human
hemoglobin has
146 amino acids
total.
Sugar glider vs. Flying squirrel
Convergent evolution
Genetic drift
Changes to allele frequencies in population due to random
chance
Bottleneck effect
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Genetic drift due to drastic reduction in allele
frequencies
What
factors can
cause
bottleneck
effect?
The founder effect
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Members from a larger population colonize an
isolated region. (Ex: primary, secondary
succession)
Ex: 15 people founded a British colony in
1814, midway in the Atlantic Ocean. One
colonist had retinitis pigmentosa, a recessive
degenerative blindness. Today, there is a
higher frequency of this disorder than most
places on Earth.
Gene flow
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Genetic exchange due to migration of
fertile individuals or gametes between
populations
Ex: wind carrying pollen grains with
sperm from plant to far off locations
Mutations
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Changes to an organism’s DNA
Changes in the DNA, if occurring in gametes,
can be passed down to the next generation.
Quantitative changes to the population can
only result if organisms with the mutation
produce a disproportionate number of
offspring.
Variations in the population
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Polymorphism: For any characteristic,
there are more than two “morphs”
(forms).
A variation of the characteristic can only
be considered one of the morphs if
there is a high enough frequency in the
population.
Measuring diversity
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Gene diversity: measuring whole
gene differences
Nucleotide diversity: measuring
differences at the molecular level (using
RFLP analysis or genomic comparisons)
Geographic diversity
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Differences in gene pools between
populations or within subgroups of
populations
Cline: graded change in some trait
along a geographic axis
Cline
What preserves variation
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Mutation
Sexual recombination (meiosis)
Diploidy
Balanced polymorphism: ability to maintain
stable allele frequency (established through
heterozygote advantage and frequencydependent selection)
Neutral variation
Directional selection
Limitations of natural selection
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1. Limited to historical constraints
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2. Adaptations are often compromises.
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3. Not all evolution is adaptive.
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4. Selection can only edit existing variations.
Hardy-Weinberg equation of
non-evolution
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No natural selection
No mutation
No migration
Large population
Random mating
p2 + 2pq + q2 = 1
p+q=1
Hardy-Weinberg equation
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p = frequency of dominant allele in the
population (A)
q = frequency of recessive allele in the
population
p2 = AA (homozygous dominant genotype)
2pq = Aa (heterozygous genotype)
q2 = aa (homozygous recessive genotype)
p2 + 2pq = dominant phenotype
q2 = recessive phenotype
Sample H-W problem
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Hint to solving these equations: LOOK FOR
THE PERFECT SQUARE!! SOLVE FOR Q!
In a population of 100 individuals, 91 in the
population show the dominant phenotype.
What is the frequency of the dominant allele
in this population?
(100 – 91)/100 = recessive phenotype = q2
.09 = q2
q = .3
p+q = 1 p = .7
The Origin of Species
In what circumstances would new
species evolve from preexisting
species?
Reproductive barriers helps to
preserve species.
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Any factors that impedes the
reproduction of members within a
species
Without the ability to breed together,
the gene pool is isolated. (no
migration)
Two types of barriers
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Prezygotic barriers: prevents
fertilization of ova (egg)
Postzygotic barriers: following
fertilization, hybrid zygote unable to
develop into viable offspring
Prezygotic barriers
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Habitat isolation
Behavioral isolation
Temporal isolation
Mechanical isolation
Gametic isolation
Postzygotic barriers
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Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Other definition of species
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Ecological: niche (set of environmental
resources an organism uses)
Pluralistic: more than one way to
define species
Morphological: organisms with unique
set of structural features
Geneological: organisms with unique
genetic history
Interrupting gene flow
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Changes to the gene pool can
ultimately lead to evolution of new
species.
This is called speciation.
Patterns of speciation
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Anagenesis:
phyletic evolution,
accumulation of
heritable change in a
population
Cladogenesis:
branching evolution,
(basis for biological
diversity)
*Three modes of speciation*
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Allopatric speciation: geographic
separation leads to new species if organisms
evolve reproductive barriers
Sympatric speciation: small population
within parent population becomes new
species
Adaptive radiation: ancestral species
colonize an area where diverse geographic or
ecological conditions are available, rapid
evolution
Allopatric vs. Sympatric
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What factors
can lead to
each type of
speciation?
Allopatric speciation
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Geographic barriers (mountains,
valleys, etc) can separate the ability for
breeding between members of the
same species.
Ring species: species that seemingly
are in the gradual process of divergence
from a common ancestor
Adaptive radiation
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Much like allopatric
speciation
Island chains have
geographic isolation but
are close enough for
occasional have hybrids
between populations.
How reproductive barriers
evolve
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Diane Dodd’s experiment showing
allopatric speciation leading to
reproductive barrier (therefore new
species)
Allopatric speciation
Sympatric speciation in plants
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Autopolyploid: organism with more than
normal chromosome # due to meiotic
failures.
4N can breed with 4N  8N offspring
(polyploid)
In one generation, postzygotic barriers form,
causing reproductive isolation.
Allopolyploid
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Members of two different species create a hybrid that
cannot back breed with parents. The hybrid is more
vigorous (*hybrid vigor*) enables hybrid to
reproduce asexually  may eventually evolve sexual
reproduction.
Sympatric speciation
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Fishes in Lake Victoria (East Africa)
demonstrate that females may select
mates based on coloration.
Overtime, the nonrandom mating
leads to behavioral isolation, and a new
species of fish arise within the parental
population.
Punctuated equilibrium
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Sudden
appearance
of
organisms
in the
phylogeneti
c tree
Micro vs. Macroevolution
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Microevolution: changes in gene (allelic)
frequency over generations; Hardy &
Weinberg
Macroevolution: level of change in
organisms that is evident in the fossil record
(requires long period of time)
Speciation bridges microevolution and
macroevolution.
Patterns of evolution
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Divergent evolution: Two or more species
originate from the same ancestral species.
Convergent evolution: Two unrelated
species share many characteristics.
Parallel evolution: Two related species
after divergence evolve similar characteristics.
Coevolution: symbiotic relationships
Origin of life
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Oldest fossils = 3.5 billion years old,
indicating maybe oldest life form 1 billion
years old
Cyanobacteria: earliest fossilized organisms
Common metabolic pathway in all organisms:
glycolysis
Primitive atmosphere: hydrogen, methane,
ammonia, water vapor (reducing atmosphere)
Chemical evolution
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1. Earth and its atmosphere formed.
2. Primordial seas formed.
3. Complex molecules synthesized.
4. Polymers and self-replicating molecules were
synthesized. (proteinoids)
5. Organic molecules were concentrated and
isoaltred into protobionts.
6. Primitive heterotrophic prokaryotes formed.
7. Primitive autotrophic prokaryotes formed.
8. Oxygen and ozone layer formed.
9. Eukaryotes formed.
Endosymbiotic theory
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Mitochondria and chloroplast have their
own circular and “naked” DNA.
M & C ribosomes similar to bacteria.
M & C divide independently much like
binary fission.
Thylakoid membranes of chloroplast
resemble membranes of cyanobacteria.
Origin of life experiments
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Oparin and Haldane: able to produce
coacervates that could take in enzymes;
predicted simple molecules form when
oxygen absent
Stanley Miller: able to synthesize simple
organic compounds with flash of electricity
(“lightning”); tested Oparin and Haldane’s
hypotheses
Melvin Calvin: complex molecules formed
from polymerization
Sidney Fox: microspheres (protenoids)
Chemical selection
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Aggregates with most stable compounds
remained.
Chemical reactions that preserved aggregates
enabled aggregates to remain.
Nonliving  living: able to store and use
energy (metabolism), able to pass on genetic
information
Hydrogen pumps
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Believed to be the first enzymatic
proteins (light-driven) to provide
coacervate energy
ETC of respiration and photosynthesis
formed
Why RNA before DNA
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RNA has extra –OH group on 2’ carbon.
It is able to bind amino acids to allow
for translation (genetic material 
protein enzymes)
Earliest organisms
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May have been heterotrophs
As O2 generated in atmosphere from
photodissociation (H2O)
H2O2 may have formed  killing off
heterotrophs
Cyanobacteria increased in gene pool,
forming ozone layer.
Aerobic respiration may have evolved.
Heterotroph-autotroph hypothesis