Download Unit 4 Evolution Study Guide There are five driving forces of

Unit 4 Evolution Study Guide
There are five driving forces of evolution:
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Genetic drift: change in allele frequencies because of chance events in small populations
Gene flow: change in allele frequencies as genes move from one population to another
Mutation: change in allele frequencies due to a random genetic change in an allele
Natural Selection: process by which characters or traits are maintained or eliminated in a population based on their
contribution to the differential survival and reproductive success of individuals
Sexual Selection: when certain individuals reproduce more than others because they have “better” characteristics.
They may not live longer, but they have more offspring.
There are three requirements for natural selection to occur:
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Variation: differences must exist between individuals
Heritability: the traits must be passed along to offspring; traits that are not inherited cannot be selected for or against
Differential reproductive success: some individuals must reproduce more than others as a result of their “better”
traits
An adaptation is a trait that helps an organism survive in its environment. If an adaptation is altered, it will affect the fitness of
the organism. Adaptations can be physical or behavioral. Remember, adaptation is a NOUN, and not a verb. You are born with
adaptations. You do NOT adapt. Populations may “adapt” as one adaptation becomes more common among the individuals in
each subsequent generation
Types of Natural Selection
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Directional: members at one end of a spectrum are selected for, and population shifts toward that end; bell curve will
move to the right or the left
Stabilizing: selection for the middle or average trait and against either extreme; reduces variation in the population;
bell curve becomes more narrow
Disruptive (diversifying): selection for the extremes of the trait and against the middle; bell curve splits into two; can
lead to speciation
Sexual: certain characters are selected for because they signal better genes for the offspring; peacock tails may be
flashy and heavy, but they signal a stronger male peacock. Ergo, female peacocks seek out the largest tails to mate
with so their offspring get the best genes available.
Artificial: human intervention chooses the traits; selective breeding
Sources of variation with a population
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Mutations: random changes in the DNA can introduce new alleles into a population; every adaptation began as an
advantageous mutation
Sexual reproduction: crossover, independent, assortment, and random gamete combinations all lead to offspring with
different gene combinations from the parents (maybe they’re better, maybe they’re worse, maybe they’re neither)
Balanced polymorphism: the maintenance of two or more phenotypic variants because both have advantages;
example – heterozygote advantage
Speciation is the process by which new species evolve
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Allopatric speciation: interbreeding stops because a physical barrier (a river, a canyon, etc) splits the population into
two. If the two populations then evolve separately and change so that they can no longer interbreed, speciation has
occurred
Sympatric speciation: interbreeding stops even though no physical prevents it
a. Polyploidy: one or more individuals mutates a higher than normal chromosome number; polyploidic
individuals cannot reproduce with nonpolyploidics; typically happens in plants
b. Balanced polymorphism: two phenotypic variants become so different that the two groups stop
interbreeding; usually a combination of disruptive and sexual selection
Adaptive radiation: rapid series of speciation events that occur when one or more ancestral species invades a new
environment.
Hardy-Weinberg equilibrium: p + q = 1; p2 + 2pq + q2 = 1. Evolution is NOT just always occurring. Population allele frequencies
will remain constant from generation to generation as long as there are no mutations, no gene flow, no genetic drift, no natural
selection, and random mating
Homologous character: traits that are similar between different species that signify a common ancestor; example – the bones
in bat wings are more similar in arrangement to the bones in a human hand than they are to the bones in a bird wing. This
suggests, among other things, a closer common ancestor to the human (which are both mammals) than the bird.
Vestigial character: character contained by an organism that is present, but no longer functionally useful; example – human
appendix or the whale pelvis
Gradualism: evolutionary change that happens as a slow and steady process
Punctuated equilibrium: evolutionary change that occurs in rapid bursts separated by large periods of no change; usually
associated with mass extinctions due to the niche vacancies left behind; example – mammals rapidly evolved to become the
largest land and ocean animal after the extinction of the dinosaur. During the cretaceous, mammalian ancestors were very
small and poor competitors with the larger dinosaur. When an asteroid collision killed the dinosaurs, niches and resources
were available to mammals that had not been previously available. Mammals experienced rapid evolution and speciation to
“fill” those spots.
Heterotroph theory: theory that describes how life evolved from prokaryotic heterotrophs
Convergent characters: traits that are similar in unrelated organisms caused by evolving in a similar habitat; example – wings
on houseflies as compared to birds or butterflies or dragonflies, etc. Same use, very different structure
Convergent evolution: two unrelated species evolve in a way that makes them more similar because they acquire a lot of
convergent characters; example – sharks and dolphins and very physically similar, but sharks are fish and dolphins are
mammals
Divergent evolution: two related species evolve in a way to make them less similar because they live in different
environments; example - DNA similarities show the hippopotamus as the closest land relative to the whale and the elephant as
the closest land relative to the manatee. However, hippos and whales are not very similar at face value, and neither are
manatees and elephants. Sufficient evidence supports the link and the common ancestry (DNA evidence, homologous
characters, behavioral similarities), but different environments have created drastically different physical traits
Taxonomy: classification of organisms based upon the presence or absence of shared characteristics; Kingdom  phylum
(division)  class  order  family  genus  species
Five Kingdom System
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Monera: all prokaryotes
Protista: single-celled eukaryotes
Plantae: multicellular autotrophs with a cell wall
Fungi: (mostly) multicellular, non-motile, saprophytic heterotrophs with a cell wall
Animalia: multicellular, motile heterotrophs without a cell wall
Six Kingdom System
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Archaebacteria: extremophile prokaryotes, more similar to the eukaryotes than typical bacteria, most similar to
the original cells based on early earth conditions, classified by extreme environmental conditions (thermophiles
live in hot places, halophiles live in salty places, methanogens produce methane as a respiration by-product,
acidophiles live in acidic environments)
Eubacteria: typical prokaryotic bacteria, classified by their mode of nutrient procurement and shape (cocci are
round, bacilli are rod-shaped, spirilli are spiral-shaped, staphylo form clusters, strepto form chains; exstaphylococcus bacteria are clustered and round)
Protista (see above)
Plantae (see above)
Animalia (see above)
Endosymbiotic theory: eukaryotes evolved from symbiotic partnerships of prokaryotic cells
Phylogenetics: tracing and reconstructing the ancestry of species by studying physical, behavioral, and genetic similarities
(phylogenetic trees); more about evolutionary history than current similarities
Cladistics: determining relatedness through derived (or similar) characteristics by comparing the traits a group of organisms
have or have lost (cladograms); more about current similarities and less about evolutionary history, but still can be used to
determine relatedness