Maryclaire O’Brien
AP Bio Study Guide
I.
BioChemistry
Functional Groups
II.
Evolution
Natural Selection
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Adaptation: organisms are ideally shaped to aid their survival & reproduction in
certain environments
Fitness: relative ability to survive & produce offspring
Principles of Natural Selection:
1. Variations of phenotypes
2. Many of these variations are heritable & can be passed on to offspring
3. Populations often have way more offspring that resources can support
4. Fitness can lead to variations in survival & reproduction rates (survival of the
fittest)
Natural selection changes the genetic composition of entire populations
Modes of Selection:
1. Directional Selection: when the favored trait is at one extreme end of traits
2. Stabilizing Selection: the medium trait is being selected for (ex. Infant birth
weight)
3. Disruptive Selection: favors traits at both extremes
Sexual Selection: struggle between individuals of the same sex to reproduce
- Directional sexual selection: individuals get mates based on their physical
attractiveness
Speciation
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Species: a group of organisms that can interbreed & produce fertile offspring
Hybrids: offspring resulting from the crossing of 2 distinct species
- Hybrids are sterile (ex. Ligers and Mules)
Speciation: how species develop & form
- Requires reproductive isolation
o Pre-zygotic isolation: changes within a species that prevent them from
reproducing
i.
Behavioral differences (i.e. different mating calls)
ii.
Geographic isolation
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o Post-zygotic isolation: parents can form a zygote together but their
offspring can’t survive and/or reproduce
Allopatric Speciation: a species evolves into 2 distinct species because of
geographical isolation
o Populations adapt to their different environments
o Lack of gene flow between the two separated populations allows for
new species to form
Sympatric Speciation: a new species forms due to reproductive isolation while
inhabiting the same geographical area
Population Genetics
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The study of how a population of a species changes genetically over time leading
to a species evolving
Population: a group of individuals of a species that can interbreed
Allele Frequency: how often certain alleles turn up within a population
5 Factors that Change a Population’s Allele Frequency:
1. Natural selection: alleles for fitter organisms become more frequent
2. Sexual Selection: alleles from more sexually attractive individuals become
more frequent
3. Mutations: new alleles pop up due to mistakes in DNA
4. Genetic Drift: an allele’s frequency changes due to random chance
i.
The smaller the population, the more likely the chance for genetic drift
5. Gene Flow: changes in allele frequency due to mixing with genetically
different populations
Hardy-Weinberg Principle: shows the frequency you can expect to find certain
alleles in a population that’s not evolving
Hardy-Weinberg Equilibrium: the frequency of alleles in a population stays
constant from generation to generation
- Rules for Equilibrium:
1. No natural selection: no alleles are more beneficial than any other
2. No sexual selection: mating within a population must be completely
random
3. No mutations
4. Large population so there’s no genetic drift
5. No gene flow
Hardy-Weinberg Equation: p^2 + 2pq + q^2 = 1 (WW; Ww: ww)
Taxonomy
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The science of classifying living things
Taxa: organized groups of organisms
Phylogenetic Tree (Tree of Life)
Species
Genus
Family
Order
Class
Phylum
Kingdom
Domain (Bacteria, Archaea, Eukarya)
Homologous Traits/Structures: stem from a common evolutionary ancestor
Binomial Nomenclature: using a unique 2-part name for every species
- Genus + species name
Bacteria & Archaea = prokaryotes
- No nucleus for genetic material
4 Kingdoms in the Eukarya domain: Protista (single-celled), Fungi, Plantae,
Animalia
Autotrophs: can feed themselves
- Plantae & some Protista
Heterotrophs: get energy from eating other organisms
- Fungi, Animalia, & some Protista