BIOSC 0160: EXAM 2 EVOLUTION AND SPECIFICATION
84 Cards in this Set
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fossil record
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all fossils that have been found and described in scientific literature
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extant species
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species living today
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transitional feature
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trait in a fossil species that is intermediate between those of older and younger species
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vestigial trait
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reduced and incompletely developed structure that has no function or reduced function
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phylogeny
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family tree of populations/ species
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genetic homology
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occurs in DNA sequences
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occurs in DNA sequences
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recognized in embryos
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structural homology
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similarity in adult morphology/ form
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similarity in adult morphology/ form
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1) the individual organisms that make up a population vary in the traits they possess, such as age and shape
2) some trait differences are heritable - passed onto offspring genetically
3) many more offspring are produced than survive to reproduce
4) the environment choose individuals …
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biological fitness
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ability of an individual to produce surviving offspring
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acclimation
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changes in an individuals phenotype that occur in response to changes in the environment
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what are the four mechanisms that shift allele frequencies in populations?
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1) natural selection
2) genetic drift
3) gene flow
4) mutation
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natural selection
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INCREASES the frequency of certain alleles - the ones that contribute to the reproductive success
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genetic drift
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allele frequencies CHANGE RANDOMLY sometimes, drift may cause alleles that decrease fitness to increase in frequency
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gene flow
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occurs when individuals leave one population, join another, and breed - allele frequencies may change because arriving individuals introduce alleles and departing ones remove alleles
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mutation
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MODIFIES allele frequencies by continually introducing new alleles - can be beneficial, detrimental, or have no effect
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gene pool
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group where all the gametes produced in one generation go
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Claims of Hardy Weinberg Equilibrium
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1) if the frequencies of A1 and A2 = p and q (alleles) then the frequencies of the genotypes will be given by p^2, 2pq, q^2
2) meiosis and random combination of gametes doesn't cause the allele frequency to change
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Important assumptions of HWE
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1) no natural selection at the gene in question
2) no genetic drift, random allele frequency change
3) no gene flow
4) no mutation
5) random mating with respect to gene in question
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codominant
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heterozygotes have both alleles
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how to estimate genotype frequency of a population?
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obtain data from a large number of individuals and then divide the number of individuals with each genotype by the total number of individuals with each genotype
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directional selection
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a mode of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population
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purifying selection
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disadvantageous alleles decline in frequency
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stabilizing selection
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a mode of natural selection that favors phenotypes in the middle of the range of phenotypic variation. Reduces genetic variation in a population
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disruptive selection
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A mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Maintains overall genetic variation in a population
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heterozygous advantage
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heterozygotes have a higher fitness than homozygous individals
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balancing selection
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no single allele has a distinct advantage and increases frequency
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when does balancing selection occur?
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1) environment varies over time of in different geographic areas occupied by population
2) frequency-dpeendent seection --> when certain alleles are favored when they are rare but not when they are common
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what causes genetic drift in populations?
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founder effect and genetic bottleneck
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founder effect
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occurs when a new population is established and there is a change in allele frequencies
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genetic bottleneck
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when a sudden change in the number of alleles in a population; drift occurs and causes a change in allele frequency
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the biological species concept
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says the critical criteria in identifying specs is reproductive isolation - no gene flow occurs between reproductively isolated populations
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pre zygotic isolation
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prevents individuals of different species from mating
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post zygotic isolation
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offspring of matings between members of different species don't survive/ reproduce
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temporal
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populations are isolated because they breed at different times
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habitat
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populations are isolated because they breed in different habitats
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behavioral
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populations dont interbreed their courtship displays differ
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gametic barrier
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matings between sperm and egg are incompatible
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mechanical
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matings fail because male and female reproductive structures are incompatible
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hybrid viability
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hybrid offspring do not develop normally and die as embryos
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hybrid sterility
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hybrid offspring mature but are sterile as adults
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hybrid offspring mature but are sterile as adults
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distinguishing features are most likely to occur if populations are independent and isolated from gene flow (only used when you can't address reproductive isolation - fossils)
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the phylogenetic species concept
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species as the smallest monophyletic group in a certain group of organisms
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synapomorphy
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a trait found in a certain group of organisms that exists in no others
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vicariance
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physical splitting of a habitat
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allopatric speciation
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speciation that begins when populations of the same species become geographically isolated via dispersal of vicariance
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allopatry
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populations that live in different areas
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sympatry
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when populations/ species live in the same geographic area to make interbreeding possible
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polyploidy
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having more than two sets of chromosomes -occurs when doubling of chromosome number during meiosis
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fertile offspring
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tetraploid and diploid rarely produce...
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autopolyploid
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state of having more than two full sets of chromosomes due to a mutation that doubled chromosome number
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allopolyploid
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individuals are created when parents that belong to different species mate and produce an offspring where chromosome number doubles
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reinforcement
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natural selection for traits that prevent interbreeding between recently diverged species
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cryptic species
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non-breeding, but morphologically very similar
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monophyletic group
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an ancestral population and its descendants
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synapomorphy
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trait unique to a monophyletic group
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trait unique to a monophyletic group
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shows the ancestor-descendant relationship between species
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branch
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represents a population through time
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node
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where two branches diverge; when an ancestral species splits into one or more descendant species
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tip
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end point of a branch; represents a group - living today or previously extinct
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phenetic approach
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based on computing a statistic that summarizes the overall similarity among populations
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cladistic approach
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based on the realization that relationships among species can be reconstructed by identifying shared derived characteristics from the species being studied
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homology
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when traits are similar due to shared ancestry
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homoplasy
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when traits are similar for other reasons than common ancestry
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convergent evolution
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occurs when natural selection favors similar solutions to the problems posed by a similar way of making a living
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parsimony
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used to reduce the chance of homoplasy leasing to erroneous conclusions
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habitat bias
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organisms that live in areas where sediments are being actively deposited are much more likely to fossilize than other animals
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example of habitat bias
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burrowing organisms such as clams
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taxonomic/ tissue bias
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slow decay is essential to fossilization; organisms with hard parts (bones + shells) are more likely to leave fossil evidence than other animals
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examples of taxonomic/ tissue bias
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clams, snails, organisms with hard parts
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temporal bias
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recent fossils are more common than ancient fossils
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example of temporal bias
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tectonic plates converging destroys fossils and older fossils are easily demolished
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abundance bias
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organisms that are abundant, widespread, and present on Earth for a long time leave evidence more often than other species
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what eons does the precambrian consist of?
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Hadean, Archean, Proterozoic
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Precambrian
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life was exclusively unicellular; oxygen was absent from oceans/ atmosphere for 2 billion years after the origin of life
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Two compelling events to study in the history of life
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1) periods when species originate/ diversity rapidly
2) period when species go extinct rapidly
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adaptive radiation
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when a single lineage produces many descendant species that live in various habitats and use various resources
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3 hallmarks of adaptive radiation
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1) they are a monophyletic group
2) they spectated rapidly
3) they diversified ecologically - resource use and habitat occupation
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niche
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range of resources and conditions a species can use
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ecological opportunity
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availability of new and novel resources
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morphological innovation
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evolution of a key morphological trait
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impact hypothesis
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an asteroid struck the earth and killed 60-80% of life
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What is the mother of mass extinctions?
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the end-permian extinction
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background extinction
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lower average rate of extinction; occurs when normal environmental change, diseases, and competition reduced certain populations to zero
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BIOSC 0160: EXAM 2 EVOLUTION AND SPECIFICATION