exam 2 Flashcards
how does gene flow effect populations?
makes population more similar
genetic isolation
occurs when a barrier to gene flow isolates two populations within a species. the alleles between the two populations are no longer exchanged
genetic divergence
occurs when mutation, natural selection, and genetic drift occur in each of the isolated populations. the isolated populations begin to evolve independently and diverge into distinct species
speciation
is the rapid or gradual evolution of two or more distinct species from a single ancestral species. in most cases it results from genetic isolation and genetic divergence.
hybrid inviability
hybrid offspring do not develop normally and die as embryos (at early development)
hybrid sterility
hybrid offspring mature but are sterile as adults
polymorphic species
two species are incorrectly identified even though it is only one. a species is spilt into two categories based on different phenotypes
cryptic species
a species that cannot be distinguished from similar species by easily identifiable morphological traits
monophyletic groups
is an evolutionary unit that includes an ancestral population and all of its descendants but no others. also called a clade or lineage. identified by traits called synapomorphies
synapomorphies
a shared, derived trait found in two or more taxa taht is present in their most recent common ancestor but is missing in more distant ancestors. are useful for inferring evolutionary relationships. researchers usually use DNA to identify these
polyploidization
the state of having more than two full sets of chromosomes, either from the same species or from different species. chromosome duplication produces mismatched chromosomes between populations and caused post-zygotic isolation. a very important particular type of mutation in speciation. there are two types: autopolyploid and allopolyploid
autopolyplod
the state of having more than two full sets of chromosomes due to a mutation that doubled the chromosome number. all the chromosomes come from the same species
allopolyploid
the state of having more than two full sets of chromosomes due to the hybridization between species.
biological species concept
the definition of a species as a population or group of populations that are reproductively isolated from other groups. members of a species have the potential to interbreed in nature to produce viable, fertile offspring but cannot interbreed successfully with members of other species. promoted by Ernst Mayr.
pre-zygotic isolation
reproductive isolation resulting from any combination of several mechanisms that prevent individuals of two different species from mating. types are: temporal, habitual, behavioral, mechanical, and gametic barriers.l
post-zygotic isolation
reproductive isolation resulting from mechanisms that operate after mating of individuals of two different species occurs. the most common mechanism are the death of hybrid embryos or reduced fitness of hybrid.
disadvantages of the biological species concept
the criterion of reproductive isolation cannot be evaluated in fossils, concept is difficult to apply, and can be a complex gradient rather than an all-or-nothing scenario
the morphospecies concept
the definition of a species as a population or group of populations that have measurably different anatomical features from the other groups. the idea that distinguishing features are most likely to arise if populations are independent and isolated. is compelling because it is widely applicable and applies equally to sexual, asexual, or fossil species
disadvantages to morphospecies concept
may lead to the naming of two or more species when there is only one, cannot identify a cryptic species, and morphological features used to distinguish species are subjective.
phylogenetic species concept
the definition of a species as the smaller monophyletic group in a phylogenetic tree. identifies species based on the evolutionary history of populations/based on common ancestry. concept is versatile because it can be applied to any population and species only have different synapomorphies if they are isolated and evolved independently
Disadvantages to phylogenetic species concept
phylogenies are only for tiny subset of populations, tends to recognize more species than the morphospecies or biological species concepts, and complicates the naming of species
allopatric speciation
speciation taht occurs when populations of the same species become geographically isolated, often due to dispersal or vicariance
dispersal
the movement of individuals from their place of origin to the location where they live and breed as adults
