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population genetics and evolution (evolution and the origin of life…
population genetics and evolution
population genetics
factors that cause the gene pool to change
mutations
due to mutations, existing alleles decrease in frequency while new alleles increase
accidents- events in which an organism cannot adapt
example- volcanic eruptions could eliminate organisms carrying special genes.
affects less well adapted organisms that well adapted ones
artificial selection- process in which humans purposefully change the alleles frequency of a gene pool
examples include selective breeding in plants
natural selection- survival of the fittest; individuals most adapted survive
2 conditions must be met in order for natural selection to occur
the populaiton must produce more offspring than can possibly grow /survive to maturity
progeny must differ from each other in their types of alleles
situations in which natural selection does not operate
cannot operate is the population is identical
if survival is universal, then natural selection cannot occur
multiple selection pressures
abundance of different alleles within a population, how they increase, decrease, or remain the same with time
gene pool: total number of alleles in all the sex cells of all individuals of a population
speciation
phyletic speciation
critical feature- new beneficial alleles arise and are selected form
gene flow- movement of alleles throughout a population
occurs by pollen transfer, seed dispersal, vegetative propagation
pollen transfer can be done via wind blowing and distributing pollen to other plants
seed dispersal can occur by rafting, seeds can stick to other animals and be distributed that way
if a species produces small mobile pieces that reproduce vegetatively, this can contribute to gene flow
divergent speciation
gene flow does not keep the species homogeneous throughout its entire range
reproductively isolated- alleles that arise in one part of the range do not reach individuals in another part
can occur abiological and biological reproductive barriers
abiological reproductive barrier- any physical, nonliving feature that prevents 2 populations from exchanging genes
allopatric or geographic speciation
any biological phenomenon that prevents successful gene flow
mutations could change the phenotype of a flower and pollinators will not recognize it
sympatric speciation- 2 groups become reproductively isolated even though they grow together
prezygotic isolation mechanisms: they act before a zygote can be formed
postzygotic internal isolation barriers- becomes distinct and subgroups can no longer interbreed; two subpopulations are separate species
hybrid sterility- earliers postzygotic barrier
2 populations occassionaly interbreed/ are artifically cross-pollinated and produce a viable seed
adaptive radiation- case of divergent evolution; species rapidly diverge into new species
convergent evolution
2 species evolve to the point they resemble each other
example- cacti
process in which a new species to evolve
rates of evolution
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evolutionary changes that result in the loss of a structure or metabolism can come about quickly
mutations that disrupted the formation of the lamina were advantageous
cacti lost their leaves in as little as 10 million years
evolution and the origin of life
conditions on earth before the origin of life
second atmosphere created by release of gases from the rock matrix
second atmosphere is a reducing atmosphere
chemicals produced chemosynthetically
formation of polymers
polymerization requires high concentration of monomers
aggregation and organization
next step in chemical evolution
aggregation of chemical components into masses that had organization and metabolism
without genetic- natural selection cannot occur
early metabolism
an aggregate capable of producing an enzyme that synthesizes molecules
matabolic pathway
oxygen
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oxidizing atmosphere- secondary atmosphere with addition of oxygen
the presence of life
this image shows an example of a gene pool
this image shows the difference between convergent and divergent speciation
this image shows how polymers are formed
evolution is present when it comes to the origins of life
evolution is also evident when it comes to adaptations of organisms and genetics
without oxygen, species would not exist
