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Where are substitutions more common?
at positions that do not change the amino acid
What does neutral mean?
don't convey a selective advantage or disadvantage
What does the molecular clock do?
helps you calculate how long it has been since two species "diverged" from a common ancestor
What is positive directional selection?
rate of non-synonymous substitution exceeds the rate of synonymous substitution
What is neutral selection?
rate of non-synonymous substitution equals the rate of synonymous substitution
What is a form of stabilizing or purifying selection?
rate of non-synonymous substitution is less than the rate of synonymous substitutions
Where is genetic drift stronger: smaller or larger populations?
small populations
What does sexual recombination lead to?
leads to genetic variability in offspring
What are some of the disadvantages of sexual reproduction?
only 50% of the female genes are passed on; recombination separates adaptive gene combinations
What are the advantages of sexual reproduction?
recombinations can separate deleterious combinations; homologous chromosomes are used to repair damaged DNA; recombination introduces genetic variation
What is the main advantage of asexual reproduction?
increased fitness
What are some of the disadvantages of asexual reproduction?
no way to eliminate deleterious mutations
What is lateral or horizontal gene transfer?
process by genes, organelles, or fragments of entire genomes move from one lineage to another
What is gene duplication?
entirely new copy of a gene appears in a genome over evolutionary time
What is a gene family?
group of homologous genes that have related functions
What is speciation?
process in which biological lineages diverge due to reproductive isolation, resulting in new species
What are sister species?
each one is the other's closest relative
What is the morphological species concept?
defines a species based on observable morphological characteristics such as body shape, size, color, and other structural features
What are some of the problems of the morphological species concept?
members of the same species may look alike; members of the different species may look similar
What is the biological species concept?
two organisms are of the same species if they can mate with one another
What is the main idea of the biological species concept?
groups of actually or potentially interbreeding natural populations that are reproductively isolated
What is reproductive isolation?
situation in which two groups of organisms are unable to exchange genes
What are the disadvantages of the biological species concept?
does not apply to asexual organisms; cannot be applied to extinct species; ring species are too distantly related to interbreed
What is the lineage species concept?
two groups that share a branch on the tree of life
What does speciation require>
requires an interruption in gene flow
What does the Dobzhansky-muller model explain?
explains how a single lineage can split into two reproductively isolated species; overtime, the two species will be unable to mix and will be considered two different species
When does reproductive isolation increase?
when a species diverges genetically
What is allopatric speciation?
population is divided by a physical or geographic barrier, forming two reproductively isolated populations that evolve independently
What is sympatric speciation?
species arise from a population that remains connected
What does disruptive selection do?
favors two extreme phenotypes and results int eh divergence between two species
What is temporal isolation?
flower at different times; breed at different times of the year
What does polyploidy mean?
mistake during cell division results in an individual with cells that have more than one copy of teh genome
autopolyploidy
duplication of a set of chromosomes in a single species
allopolyploidy
chromosomes of two different species are combined
incipient species
species that are in the process of diverging into separate species, but can currently interbreed
What is a prezygotic isolating mechanism?
prevents hybridization; prohibits individuals of different species from attempting to mate
What is mechanical isolation?
some animals are simply not physically compatible with other animals due to anatomical differences
What is temporal isolation?
never have the opportunity to reproduce with the other due to the timing of reproduction
What is behavioral isolation?
pairing of mates does not occur unless the correct mating rituals or signals are performed (certain frogs will only mate with individuals who make a specific kind of mating call)
habitat isolation
some animals are isolated by space such that they never have the opportunity to come into contact with one another
What is gametic isolation?
some animals produce sperm and eggs that simply will not fuse when they come into contact (important in aquatic communities)
What is a postzygotic isolating mechanism?
reproductive barriers that prevent interbreeding after the development of the zygote; reduce the fitness of the hybrid offspring
What are some of the post-zygotic mechanisms?
reduced genetic compatibility; low hybrid zygote viability; low adult hybrid viability; hybrid infertility
Why does natural selection tend to favor pre-zygotic mechanisms?
it is easier to prevent reproduction from occurring in the first place
Where are pre-zygotic reproductive barriers stronger?
populations living in sympatry have stronger reproductive barriers because they prevent hybridization from occurring (hybridization already occurs in allopatric speciation)
What does a phylogeny do?
describes the evolutionary history of the relationships between living things
What is a node?
point where two branches separate
What does the root represent in a phylogenetic tree?
common ancestor that all organisms share
What may or may not mean something on a phylogenetic tree?
branch length
What is special about the order of things on a phylogenetic tree?
nodes can spin around; you can swivel the branches at the top node without changing the relationships
What is a taxon?
group of species with a name
What is a sister species?
species that directly evolve from a common ancestor
monophyletic clades
groups of taxa that include an ancestor and all of its descendants
What are sister clades?
two clades that are each other's closest relatives
what is systematics?
study and classification of biodiversity
What is homology?
any heritable trait shared by more than one species and inherited from a common ancestor
What is a derived trait?
evolved from an earlier condition
What is a synapomorphy?
shared, derived traits that provide evidence of common ancestry
What is special about the relationship of homology and synapomorphy?
all synapomorphies are homologous but not all homologies are snapomorphies
What are homoplasies a result of?
convergent evolution or evolutionary reversal
What are homoplasies?
traits that are shared not due to evolutionary history but rather because fo convergent evolution or evolutionary reversals
What is convergent evolution?
similar traits evolve in different lineages; share homoplasies that are common to the different species but have independent evolutionary origins
What homoplasies commonly lead to?
false or incorrect conclusions
What is evolutionary reversal?
character reverts from a derived state back to an ancestral state
What is the goal of a phylogeny?
parsimony principle; simplest explanation for observed date is the best explanation; eliminates the number of evolutionary changes and homoplasies in the tree
What is the outgroup?
species closely related to the ingroup, but not closely related enough the be inside the group of interest
What is the purpose of the outgroup?
outgroup provides something to compare to and see where/when traits evolved
What is the ingroup?
groups of organisms we are interested in
What are ancestral traits?
traits of the ingroup that are the same in the outgroup
What are derived traits?
traits are different from those in the outgroup
What is morphology used for?
way to classify extinct species
What is a disadvantage of behavior?
it is hard to measure behavior and it is greatly influenced by the environment
What does a molecular clock do?
groups the # of nucleotide differences against the times of a series of evolutionary branch points that are known from the fossil record or known times of divergence
What is the order of classification?
King Philip Came Over For Good Sex
What is a monophyletic grouping?
contains an ancestor and all of its descendants
What is paraphyletic grouping?
contains teh ancestor and some of its descendants
What is polyphyletic grouping?
does not contain its common ancestor
What is stratigraphy?
determine how old a rock is compared to other rocks
What is a sedimentary rock?
top layers are newer and bottom layers are older
What does an actual dating method measure?
determines the actual age of teh rock
What does carbon dating do?
determines how old organic matter is (must be 60000 years old or younger)
How are igneous rocks formed)
rocks are formed when the molten rocks cool
What is radiometric dating?
determines how old something is based on the proportion of radioactive isotopes to normal isotopes found in it
What is a major disadvantage of fossils?
most organisms do not fossilize; many fossils are destroyed over time and are not ever found
What is continental drift?
movement of the Earth's plates, which produces significant change in the physical environment
What is speciation?
formation of new and distinct species in the course of evolution
What often declines as the globe cools and more glaciers form?
sea levels decline
What are stromatolites?
contain living colonies of cyanobacteria
What does decay require?
requires oxygen
What was the cambrian explosion?
huge diversification of multiceulluar life
What happened during the permian period?
continents collide to form pangea
What happened during the cretaceous period?
mass extinction due to a meteorite
Which selection reduces variance without changing the mean value of a trait?
stabilizing selection
What selection changes the mean while not changing the variance?
directional selection
What selection changes the variance but may or may not change the mean?
disruptional selection
What selection creates a bimodal distribution?
disruptional selection
What selection favors the intermediate value?
stabilizing selection
Which selection favors one extreme?
directional selection
Which selection favors both extremes?
disruptional selection
What selection favors the common phenotype?
positive selection
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