25- speciation pt3 Flashcards
why may sympatric speciation (mutations) occur in plants?
errors during meiosis and mitosis
i.e. the production of a diploid gamete producing triploid offspring
what is a triploid offspring?
if a diploid gamete is fertilized by a haploid gamete the offspring will be triploid (meiosis error)
why are triploid individuals sterile?
homologous chromosomes cannot line up during meiosis 1
can triploid plants reproduce?
they can only spread vegetatively, via fragmentation, solons or saplings
how can triploid plants lead to speciation if they cant produce gametes?
if a triploid egg is produced via another error in meiosis and it is fertilized by a haploid sperm, the offspring becomes tetraploid (4n)
they can produce gametes but are reproductively isolated from their original population = speciation is likely.
why do hybrid embryos survive but hybrids are often sterile?
the two chromosomes are from two different species so they cannot line up during meiosis 1
what is alloploidy?
polyploidy which results from chromosomes from other species (plants only) from tetraploid genes
what are tetraploid hybrids likely to evolve into?
a new species
what percent of angiosperms (plants) are of polyploid origin?
50-70%
what are benefits of polyploidy in plants?
increased vigor, gene redundancy, shields from the deleterious effect of mutations, and asexual reproduction is often more common
what are prezygotic barriers?
mechanisms that block reproduction from taking place before the zygote is formed
examples of prezygotic barriers
-habitat isolation
-temporal isolation
-behavioral isolation
-gametic barrier
-mechanical isolation
-pollinator isolation/floral isolation
-hybrid inviability
-hybrid sterility
what is adaptive radiation?
rapid speciation from a small number of species into numerous different species
what is the hybrid zone?
the geographic area where two closely related species continue to interact and reproduce
what is reinforcement hybrid zone
hybrids less fit than either purebred species. the species continue to diverge until hybridization can no longer occur
what is fusion hybrid zone?
reproductive barriers weaken until the two species become one
what is stability hybrid zone?
fit hybrids continue to be produced
what are the two rates of speciation
gradual
punctuated equilibrium
what is punctuated equilibrium
a new species undergoes changes quickly from the parent species, and then remains largely unchanged for a long time
what type of speciation is likely to occur in favorable conditions?
gradual
