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BIOSC 0160: EXAM 2 EVOLUTION AND SPECIFICATION

fossil record
all fossils that have been found and described in scientific literature
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extant species
species living today
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transitional feature
trait in a fossil species that is intermediate between those of older and younger species
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vestigial trait
reduced and incompletely developed structure that has no function or reduced function
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phylogeny
family tree of populations/ species
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genetic homology
occurs in DNA sequences
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occurs in DNA sequences
recognized in embryos
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structural homology
similarity in adult morphology/ form
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similarity in adult morphology/ form
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 with certain characteristics to reproduce - natural selection
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biological fitness
ability of an individual to produce surviving offspring
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acclimation
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?
1) natural selection 2) genetic drift 3) gene flow 4) mutation
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natural selection
INCREASES the frequency of certain alleles - the ones that contribute to the reproductive success
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genetic drift
allele frequencies CHANGE RANDOMLY sometimes, drift may cause alleles that decrease fitness to increase in frequency
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gene flow
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
MODIFIES allele frequencies by continually introducing new alleles - can be beneficial, detrimental, or have no effect
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gene pool
group where all the gametes produced in one generation go
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Claims of Hardy Weinberg Equilibrium
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
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
heterozygotes have both alleles
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how to estimate genotype frequency of a population?
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
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
disadvantageous alleles decline in frequency
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stabilizing selection
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
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
heterozygotes have a higher fitness than homozygous individals
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balancing selection
no single allele has a distinct advantage and increases frequency
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when does balancing selection occur?
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?
founder effect and genetic bottleneck
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founder effect
occurs when a new population is established and there is a change in allele frequencies
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genetic bottleneck
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
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
prevents individuals of different species from mating
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post zygotic isolation
offspring of matings between members of different species don't survive/ reproduce
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temporal
populations are isolated because they breed at different times
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habitat
populations are isolated because they breed in different habitats
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behavioral
populations dont interbreed their courtship displays differ
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gametic barrier
matings between sperm and egg are incompatible
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mechanical
matings fail because male and female reproductive structures are incompatible
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hybrid viability
hybrid offspring do not develop normally and die as embryos
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hybrid sterility
hybrid offspring mature but are sterile as adults
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hybrid offspring mature but are sterile as adults
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
species as the smallest monophyletic group in a certain group of organisms
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synapomorphy
a trait found in a certain group of organisms that exists in no others
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vicariance
physical splitting of a habitat
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allopatric speciation
speciation that begins when populations of the same species become geographically isolated via dispersal of vicariance
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allopatry
populations that live in different areas
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sympatry
when populations/ species live in the same geographic area to make interbreeding possible
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polyploidy
having more than two sets of chromosomes -occurs when doubling of chromosome number during meiosis
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fertile offspring
tetraploid and diploid rarely produce...
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autopolyploid
state of having more than two full sets of chromosomes due to a mutation that doubled chromosome number
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allopolyploid
individuals are created when parents that belong to different species mate and produce an offspring where chromosome number doubles
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reinforcement
natural selection for traits that prevent interbreeding between recently diverged species
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cryptic species
non-breeding, but morphologically very similar
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monophyletic group
an ancestral population and its descendants
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synapomorphy
trait unique to a monophyletic group
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trait unique to a monophyletic group
shows the ancestor-descendant relationship between species
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branch
represents a population through time
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node
where two branches diverge; when an ancestral species splits into one or more descendant species
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tip
end point of a branch; represents a group - living today or previously extinct
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phenetic approach
based on computing a statistic that summarizes the overall similarity among populations
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cladistic approach
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
when traits are similar due to shared ancestry
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homoplasy
when traits are similar for other reasons than common ancestry
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convergent evolution
occurs when natural selection favors similar solutions to the problems posed by a similar way of making a living
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parsimony
used to reduce the chance of homoplasy leasing to erroneous conclusions
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habitat bias
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
burrowing organisms such as clams
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taxonomic/ tissue bias
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
clams, snails, organisms with hard parts
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temporal bias
recent fossils are more common than ancient fossils
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example of temporal bias
tectonic plates converging destroys fossils and older fossils are easily demolished
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abundance bias
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?
Hadean, Archean, Proterozoic
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Precambrian
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
1) periods when species originate/ diversity rapidly 2) period when species go extinct rapidly
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adaptive radiation
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
1) they are a monophyletic group 2) they spectated rapidly 3) they diversified ecologically - resource use and habitat occupation
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niche
range of resources and conditions a species can use
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ecological opportunity
availability of new and novel resources
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morphological innovation
evolution of a key morphological trait
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impact hypothesis
an asteroid struck the earth and killed 60-80% of life
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What is the mother of mass extinctions?
the end-permian extinction
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background extinction
lower average rate of extinction; occurs when normal environmental change, diseases, and competition reduced certain populations to zero
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