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AP Biology Exam Review2002-2003
Heredity and Evolution – 25%
Evolutionary biology – 8% Early evolution of life Evidence of evolution Mechanisms of evolution
Related fields of study 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 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 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
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 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
Human hemoglobin has 146 amino acids total.
Sugar glider vs. Flying squirrel
Convergent evolution
Genetic driftChanges to allele frequencies in population due to random chance
Bottleneck effect Genetic drift due to drastic reduction in
allele frequencies
What factors can cause bottleneck effect?
The founder effect 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 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 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 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 Gene diversity: measuring whole
gene differences
Nucleotide diversity: measuring differences at the molecular level (using RFLP analysis or genomic comparisons)
Geographic diversity 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 Mutation Sexual recombination (meiosis) Diploidy Balanced polymorphism: ability to
maintain stable allele frequency (established through heterozygote advantage and frequency-dependent selection)
Neutral variation
Directional selection
Limitations of natural selection 1. Limited to historical constraints
2. Adaptations are often compromises.
3. Not all evolution is adaptive.
4. Selection can only edit existing variations.
Hardy-Weinberg equation of non-evolution No natural selection No mutation No migration Large population Random mating
p2 + 2pq + q2 = 1 p + q = 1
Hardy-Weinberg equation 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 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. 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 Prezygotic barriers: prevents
fertilization of ova (egg)
Postzygotic barriers: following fertilization, hybrid zygote unable to develop into viable offspring
Prezygotic barriers Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Gametic isolation
Postzygotic barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown
Other definition of species 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 Changes to the gene pool can
ultimately lead to evolution of new species.
This is called speciation.
Patterns of speciation Anagenesis:
phyletic evolution, accumulation of heritable change in a population
Cladogenesis: branching evolution, (basis for biological diversity)
*Three modes of speciation* 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 What
factors can lead to each type of speciation?
Allopatric speciation 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 Much like allopatric
speciation
Island chains have geographic isolation but are close enough for occasional have hybrids between populations.
How reproductive barriers evolve Diane Dodd’s experiment showing
allopatric speciation leading to reproductive barrier (therefore new
species)
Allopatric speciation
Sympatric speciation in plants 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 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 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 Sudden
appearance of organisms in the phylogenetic tree
Micro vs. Macroevolution 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 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 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 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 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 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 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 Believed to be the first enzymatic
proteins (light-driven) to provide coacervate energy
ETC of respiration and photosynthesis formed
Why RNA before DNA 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 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