This cheat sheet covers the key concepts of AP Biology Unit 5, focusing on the processes and patterns of evolution and the resulting biodiversity on Earth. Remember that this is a supplement to your textbook and class notes – not a replacement!
I. Mechanisms of Evolution
A. Genetic Variation: The raw material for evolution. Sources include:
- Mutation: Changes in DNA sequence. Can be beneficial, harmful, or neutral.
- Sexual Reproduction: Shuffles existing alleles through independent assortment, crossing over, and random fertilization.
- Gene Flow: Movement of alleles between populations. Increases genetic variation within a population but can decrease differences between populations.
B. Hardy-Weinberg Equilibrium: A null hypothesis for evolution. A population in equilibrium shows no change in allele frequencies over time. The conditions for equilibrium are:
- No Mutation: No new alleles are introduced.
- Random Mating: Individuals mate without preference for certain genotypes.
- No Gene Flow: No migration into or out of the population.
- No Genetic Drift: The population is large enough to avoid random fluctuations in allele frequencies.
- No Natural Selection: All genotypes have equal survival and reproductive success.
C. Mechanisms of Evolutionary Change (violations of Hardy-Weinberg):
- Natural Selection: Differential survival and reproduction based on heritable traits. Leads to adaptation. Types include:
- Directional Selection: Favors one extreme phenotype.
- Stabilizing Selection: Favors the intermediate phenotype.
- Disruptive Selection: Favors both extreme phenotypes.
- Genetic Drift: Random changes in allele frequencies, particularly pronounced in small populations. Includes:
- Bottleneck Effect: A drastic reduction in population size reduces genetic diversity.
- Founder Effect: A small group establishes a new population, carrying only a subset of the original population's alleles.
- Gene Flow: Movement of alleles between populations. Can introduce new alleles or alter existing allele frequencies.
II. Speciation and Macroevolution
A. Speciation: The formation of new and distinct species. Requires reproductive isolation:
- Prezygotic Barriers: Prevent mating or fertilization. Examples include habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation.
- Postzygotic Barriers: Prevent viable or fertile offspring. Examples include reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.
B. Modes of Speciation:
- Allopatric Speciation: Geographic isolation leads to reproductive isolation.
- Sympatric Speciation: Reproductive isolation occurs within the same geographic area. Can be driven by polyploidy, habitat differentiation, or sexual selection.
C. Macroevolution: Evolutionary change above the species level. Includes:
- Adaptive Radiation: Rapid diversification of a lineage into many ecologically diverse species.
- Extinction: The complete disappearance of a species. Background extinction is a continuous, low-level extinction rate; mass extinctions are periods of elevated extinction rates.
- Gradualism: Evolutionary change occurs slowly and steadily over time.
- Punctuated Equilibrium: Evolutionary change occurs in short bursts followed by long periods of stasis.
III. Phylogenetic Trees and Biodiversity
A. Phylogenetic Trees: Diagrams that depict the evolutionary relationships between species or groups of species. Key concepts include:
- Rooted vs. Unrooted Trees: Rooted trees indicate a common ancestor; unrooted trees only show relationships.
- Nodes: Represent common ancestors.
- Branches: Represent lineages.
- Clades: Groups of species that share a common ancestor.
- Monophyletic, Paraphyletic, Polyphyletic: Terms describing the evolutionary relationships within a group.
B. Biodiversity: The variety of life at all levels of biological organization. Includes:
- Genetic Diversity: Variation in genes within a species.
- Species Diversity: The number and abundance of species in a community.
- Ecosystem Diversity: The variety of ecosystems within a region.
This cheat sheet provides a concise overview of AP Biology Unit 5. Remember to consult your textbook, class notes, and practice problems for a thorough understanding of these concepts. Good luck with your studies!
