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natural selection
A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
genetic drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.
Darwin's observations in the Galapagos
Organisms on the same continent were more similar that organisms living in the same temperature, organisms that existed on islands were different from related organisms on the mainland (some were endemic -- only existed-- to that island), and animals living on different islands had different traits.
fitness
Ability of an organism to survive and reproduce in its environment
adaptations
traits that improve an individual's ability to survive and reproduce
forces of evolution that generate variation
mutation and migration
forces of evolution that reduce variation
selection and non-random mating
mutation
heritable changes in genetic information that occur in individuals
fixation
when one allele is lost and the other becomes the only one present in the population
the bottleneck effect
A change in allele frequency following a dramatic reduction in the size of a population
the founder effect
change in allele frequencies as a result of the migration of a small subgroup of a population
gene flow
migration - movement of alleles from one population to another
random mating
individuals choose their mates without any preference for particular genotypes and phenotypes
sexual selection
when individuals select mates based on heritable traits
directional selection
occurs when natural selection favors one of the extreme variations of a trait
stabilizing selection
Natural selection that favors intermediate variants by acting against extreme phenotypes (decreases variation)
disruptive selection
favors individuals at both extremes of the phenotypic range; intermediate trait is selected against. can cause polymorphism
Polymorphism
more than one stable, discrete phenotype
heterozygote advantage
occurs when heterozygotes have a higher fitness than both homozygotes (sickle cell and malaria)
Geographic variation in natural selection
natural selection act in different ways on populations that live in different geographic regions
Frequency dependent selection
the fitness of a phenotype depends on how common it is in the population (left and right mouthed fish)
artificial selection
Selection by humans for breeding of useful traits from the natural variation among different organisms
phenotypic variation =
genetic variation + environmental variation
Heritability
the fraction of variability that is due to genetic differences
positive selection
the rate of nonsynonymous substitutions exceed the rate of synonymous substitutions causing a directional shift that favors the spread of beneficial alleles
neutral selection
the rate of nonsynonymous substitutions equal the rate of synonymous substitutions causing random changes in the gene pool
negative/purifying selection
the rate of nonsynonymous substitutions is less than the rate of synonymous substitutions causing, causing stabilizing selection
Phylogeny
Evolutionary history of a species
lineage
Group claiming a common ancestor
taxon
group or level of organization into which organisms are classified
sister species
two species that are each other's closest relatives -- directly evolve from a common ancestor
clades
A group of species that includes an ancestral species and all its descendants.
homology
any heritable trait shared by more than one species and inherited from a common ancestor
synapomorphies
shared derived characters that provide evidence of common ancestry
convergent evolution
Process by which unrelated organisms independently evolve similarities (analogous characters) when adapting to similar environments
evolutionary reversal
the reversion of a derived character state to its ancestral state
Parisomony principle
the simplest explanation for observed data is the best explanation
monophyletic grouping
made up of an ancestral species and all of its descendants and no other species (same as monophyletic clade)
paraphyletic grouping
consists of an ancestral species and some, but not all, of the descendants ("repitles")
polyphyletic grouping
consists of various species that lack a common ancestor ("warm-blooded")
speciation
Formation of new species via reproductive isolation
species
a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding; unit for measuring biodiversity
morphological species concept
A definition of species in terms of measurable anatomical criteria. Problems: polymorphism (same species, different features) and cryptic species (look alike, but don't interbreed)
biological species concept
Species is a group of populations whose members have the potential to produce fertile offspring. Problems: doesn't apply to asexual organisms, cannot be applied to extinct species, and doesn't take into consideration species that can hybridize
lineage species concept
species as branches on a phylogeny
species complex
A grouping of very closely related species
Hardy-Weinberg equilibrium conditions
no mutations, random mating, no natural selection, extremely large population size, no gene flow
intersexual selection
Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.
allopatric speciation
The formation of new species in populations that are geographically isolated from one another.
cryptic species
members of different species look alike but do not interbreed
Dobzhansky-Muller Model
split, mutate, fixation, incompatibility - A population is subdivided and then the two groups evolve independently. In each lineage, new alleles become fixed at different loci. The new alleles at the two loci are incompatible with one another. Genetic incompatibility between the two isolated populations will develop over time.
allopatric speciation
the process of speciation that occurs with geographic isolation
sympatric speciation
The formation of new species in populations that live in the same geographic area caused by disruptive selection, ecological speciation, polyploidy, temporal isolation, and behavioral isolation.
temporal isolation
form of reproductive isolation in which two populations reproduce at different times
behavioral isolation
Form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding