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Population Genetics and Evolution (Speciation (divergent speciation…
Population Genetics and Evolution
Population Genetics
Gene Pool
Factors that cause the gene poole to change
mutation
occur continually
existing alleles decrease in frequency
new alleles increase
accidents
events that an organism cannot adapt
volcanic eruption
flood/ drought
artificial selection
human intervention
purposely change alleles in gene pool
selective breeding
natural selection
most significant factor
most adapt survive
population must produce more offspring than can survive to maturity
progeny must differ from each other (types of alleles)
survival of the fittest
factors that are not part of natural selection
purpose
intention
planning
voluntary decision making
Situations in which Natural Selection Does Not Operate
if all individuals in a population are genetically identical
if impossible to adapt to a certain situation
if survival is universal
Multiple Selection Pressures
loss of individuals/reduced reproduction
not caused by single factor
pathogens
drought
insects
temperature change
pollinators
mechanism to disperse seeds
Rates of Evolution
most populations already well adapted
difficult to identify particular alleles
easily identifiable if phenotype is affected
evolution studies concern gross structures
flowers
leaves
fruits
shoots
trichomes
very few mutations produce a superior phenotype
Speciation
population change resulting in new species
no longer produce fertile offspring when crossed
freely interbreed in nature=same species
do not interbreed even artificially=separate species
do not interbreed naturally but interbreed artificially=judgement call
phyletic speciation
one species
gradually becomes a new species
gene flow
movement of alleles
pollen transfer
wind-distributed
animal-mediated
seed dispersal
wind
flood
stream flow
rafting
adhesive spines/sticky
vegetative propagation
small mobile
reproduce vegetatively
divergent speciation
population diverges
into a new, second species
others in population can be unchanged
or become a new, third species
reproductively isolated
alleles in one range do not reach another range
abiological reproductive barriers
physical/nonliving feature
allopatric/geographic speciation=speciation results
biological reproductive barriers
any biological phenomenon
discriminating pollinators
differences in flowering times/date
sympatric speciation
two groups reproductively isolated
even though they grow together
prezygotic isolation mechanisms
act before zygote can be formed
postzygotic internal isolation barrier
subpopulations can no longer interbreed
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evolutionary changes in pollinators
adaptive radiation
species rapidly diverges into many species
extremely short time
little/no competition in new habitat
few selective agents
new alleles build up rapidly
genetic drift
subject to accidents
gene pool change rapidly/erratically
founder individual(s)
offspring greatly resemble the first
gene pool extremely small
Convergent Evolution
Two distinct unrelated species
occupy the same/similar habitats
may favor same phenotypes in each species
cacti
evolved from leafy trees in the Americas
euphorbias
evolved in Africa
Two groups cannot converge to same species
Evolution and the Origin of Life
chemosynthesis
The Presence of Life
chemosynthetic theory=hypothesis of the origin of life
slow/gradual transitions
inorganic compounds ----->living bacteria
chemosynthesis model
using only known chemical/ physical processes
rejects divine intervention
proposed by A. Oparin in 1924
Conditions on Earth Before the Origin of Life
approximately 4.6 Billion years ago
Conditions on Earth Before the Origin of Life
Chemicals Present in the Atmosphere
second atmosphere
produced from gases in rock matrix
meteorites
molecular oxygen absent
combined with other elements
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both sources provided
H₂S
NH₃
still found in volcanic gases &
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CH₄
Earth condensed from gases/dust
composed mostly of hydrogen
light gas (hydrogen) lost to space
Energy Sources
Sun
UV/Gamma radiatioin
knock electrons from atoms
creating reactive free radicals
Heat
coalescence of gas/dust
radioactive decay from heavy elements
Electricity
large amounts of lightning
Time Available for the Origin of Life
no limits from lack of O₂
lack of agent to breakdown created chemicals
Chemicals Produced Chemosynthetically
S. Miller 1953
container
boiling water in bottom
reducing atmosphere in the top
electrodes(stimulate lightning)
cycled for a week
became dark color
complex organic compounds formed
contained amino acids
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Formation of Polymers
concentration of monomers
seaside pools
evaporation
water freezing
absorption by clay particles
organic molecules adhere to them
specific orientation
Aggregation and Organization
chemical components w/organization and metabolism
like molecules automatically accumulate
hydrophobic material
hydrophilic materials
molecules w/ hydrophilic & hydrophobic regions
Early Metabolism
heterotrophs
absorbing all material from ocean
modifying few molecules
glycolysis
must have evolved early
present in almost all organisms
Oxygen
evolution of chlorophyll a
O₂ released as waste product
approximately 2.8 billion years ago
oxidizing atmosphere
derived from early second atmosphere
addition of O₂ from photosynthesis
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period of rusting
kept free O₂ low
toxic w/out correct mechanisms
UV light + O₂ = Ozone layer