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Population Genetics & Evolution (evolution & the origin of life…
Population Genetics & Evolution
population genetics
deals w/ the abundance of different alleles within a population
& the manner in which the abundance of a particular allele increases, decreases, or remains the same
gene pool
total # of alleles in all the sex cells of all individuals of a population
factors that cause gene pool to change
mutations: genomes are subjected to mutagenic factors, & mutations occur continually
accidents: events where an organism cannot adapt
artificial selection
process in which a human purposefully changes the allele frequency of a gene pool
natural selection
individuals that are most adapted to an environment stay, & the less adapted do not
most significant factor causing gene pool changes
factors not part of natural selection
intention
purpose
planning
voluntary decision making
situation in which natural selection does not operate
a population that is identical genetically
competition
multiple selection pressures
loss of individuals & reduced reproduction are caused by multiple factors
fungus, insect attacks, drought, cold, need for pollinators
rates of evolution
speciation
natural selection causes a new species to evolve
two ways this can occur
phyletic speciation
one species gradually becomes so changed it must be considered a new species
gene flow
movement of alleles physically through space
divergent speciation
reproductively isolated
two regions where if alleles that arise in one part of the range do not reach individuals in another part
divergent speciation
some populations of a species evolve into a new, second species while other populations either continue unchanged, parental species, or evolve into a new third species
abiological reproductive barrier
any physical, nonliving feature that prevents 2 populations from exchanging genes
original species is divided in 2 or more populations can not interbreed
allopatric/geographic speciation
if speciation results
biological reproductive barrier
any biological phenomenon that prevents successful gene flow
smpatric speciation
2 groups become reproductively isolated even though they grow together
prezygotic isolation mechanisms
bio. reproductive barrier acts. before zygote can be formed
postzygotic internal isolation barriers
prevents successful interbreeding of 2 populations but that act after fertilization; 2 sets of chromosomes are not able to produce a fertile adult
hybrid sterility
2 populations occasionally interbreed or are artificially cross-pollinated & produce viable seed, but seed grows to be sterile
hybrid inviability
much like previous step but a sterile hybrid does not result, instead the zygote or embryo dies in early development
adaptive radiation
special case of divergent evolution; a species rapidly diverges into many new species over an extremely short time (few million years)
genetic drift
gene pool can change rapidly & erratically
unrelated species occupy the same or similar habitats, & natural selection may favor the same phenotypes in each
as a consequence, the 2 may evolve to the point that they resemble each other strongly and have undergone
convergent evolution
evolution & the origin of life
chemosynthesis
most seriously considered hypothesis about the origin of life
attempts to model the origin of life using only known chemical & physical processes
conditions before origin of life
hydrogen is such a light gas that most of the first layer was lost into space
second atmosphere
produced by release of gases from rock matrix
reducing atmosphere
early 2nd atmosphere lacked molecular oxygen & presence of powerful reducing agents
chemicals produced chemosynthetically
set of experiments that explain the theoretical possibilities of direct analysis of meteorites & lunar samples reveals what has actually happened in nonliving environments
formation of polymers
monomers present in early the ocean had to polymerize if life were to arise
polymers could occur in intense sunlight
very cold water that has not yet frozen could produce a class of polymers distinct from those formed by evaporation at high temperature
aggregation & organization
next step in the possible chemical evolution of life would have been aggregation of chemical components into masses that had some organization & metabolism
the first aggregates would have been formed at random, controlled only by relative solubility
these would be complete heterotrophs & not meant to be alive bc a means of storing genetic info did not exist
at some point aggregate formed that did have inheritable info molecule able to direct the synthesis of products useful to the aggregate
early metabolism
a 2 step long metabolic pathway involving 2 enzymes was created to synthesis the scarce molecule
being able to synthesis the scare molecule would have given the aggregate a great advantage over the others; it could have a more rapid metabolism to grow & reproduce more rapidly
oxygen
evolution of chlorophyll a & photosynthesis that liberates O2 had 2 consequences
1) it allowed the world to rust 2) it created conditions that selected for the evolution of aerobic repiration
oxidizing atmosphere
atmosphere present today was derived from the early 2nd atmosphere by the addition of O2 from photosynthesis
presence of life
chemosynthetic theory postulates a long series of slow, gradual transitions from completely inorganic to living bacteria
it is difficult to say at which stage life appeared bc there is not a clear line drawn bwtn what is living & nonliving within this theory
the physics of nonliving & living systems is identical
