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Population Genetics and Evolution Ch. 17 (Evolution and the Origin of Life…
Population Genetics and Evolution Ch. 17
Population Genetics
Factors that Cause the Gene Pool to Change
Mutation
occur continually
existing alleles decrease in frequency
new alleles increase
significance depends on population size
Accidents
events when organism cannot adapt
large accidents
examples
volcanic eruption
infrequent floods
hailstroms
droughts
meteorite collision w/Earth
alleles in region are destroyed
life in area killed
large bodies strong may survive
large bodies weak die off
small accidents
examples
highway construction
avalache
herd of grazing animals
Artificial Selection
humans purposely change allele frequency of a gene pool
examples
selective breeding of crops
resistant to drought
increase protein content of seed
survive less water & fertilizer
selective breeding of domestic animals
produce ornamental plants
alter flower color
carried out in conjunction w/artificial mutation
mutagens
acridine dyes
irradiation
w/ultraviolet light
gamma rays
Natural Selection
most significant factor causing gene pool changes
survival of the fittest
individuals most adapted to environment survive
individuals less adapted do not survive
Two conditions must be met
Population must produce more offspring than can grow & survive in habitat
ex: plant seeds
Progeny must differ from each other in allele type
must be able to face adversity differently
diversity
differential survival
ex: resitant to fungi
survive
nonresistant die
can only act on preexisting alleles
does not cause mutations
Factors that Are Not Part of Natural Selection
Situations in which Natural Selection Does Not Operate
population identical genetically
impossible to adapt to certain condition
survival is universal
plowed field
side of road cut
burned area
flooded plain rich in sediments
Multiple Selection Pressures
loss of individuals & reduced reproduction are caused by many factors
pathogenic fungus
insect attack
drought
cold
need for pollinators
need for seed dispersal mechanism
efficiency of metabolism
membrane pump ions
reduce nitrogen
producing enough P-protein in phloem
new allele for trait may not survived if killed off
cold hardiness allele may be killed by fungus or drought
does not include
purpose
intention
planning
voluntary decision making
deals w/abundance of diff alleles w/in a population
the manner in which the abundance of a particular allele increases, decrease, or remains the same w/time
gene pool
total # of alleles in all the sex cells of all individuals of a population
Rates of Evolution
allelic composition of population typically does not change rapidly
most populations relatively adapted to their habitat
as systems become more intricate, probability decreases that random changes are beneficial
evolutionary change
result in loss of a structure or metabolism
can come quickly
complexity
mutations disrupt development, become selectively advantageous
ex: cacti and thin leaves
Speciation
Phyletic Speciation
Pollen Transfer
pollen grains each carry on full haploid genome
alleles of a plant are present here
can be carried great distances
wind-distributed
animal-mediated pollination
birds
insects
Seed Dispersal
seeds & fruits
carried by
wind
floods
stream flow
rafting
stick to animal
spiny
gummy
allows to spread to new site
Vegetative Propagation
small, mobile pieces that reproduce vegetatively
contribute to gene flow
species remain relatively homogeneous
mechanisms sufficient enough to enable alleles to travel to other parts
alleles that arise @ various geographic sites, ultimately come together by gene flow
meiosis
crossing over
genetic recombination rearrange them into thousands of combinations
one species gradually becomes so changed that it must be considered a new species
gene flow
movement of alleles physically through space
Divergent Speciation
Abiological Reproductive Barriers
physical & nonliving feature that prevents two pops from exchanging genes
abiological reproductive barrier
original species divided two or more pops
cannot interbreed
if speciation occurs
allopatric
geographic speciation
examples
mountain ranges
rivers
deserts
oceans
Biological Reproductive Barriers
prevents successful gene flow
differences can be effective barriers in species
examples
color
shape
fragrance
timing
flowering date
prevent pollinators from recognizing them
sympatric speciation
two groups become reproductively isolated, even though grow together
ex: Mimulus lewissi and M. cardenalis flower
evolutionary changes in pollinators
pollen prevented from moving to one plant to other
prezygotic mechanisms
subpopulations can no longer breed
postzygotic internal isolation barriers
hybrid sterility
two pops occasionally breed
artificially cross-pollinated & produce viable seed
seed grows into sterile plant
hybrid inviability
zygote or embryo dies during early development
divergent evolution
results in new species
Adaptive Radiation
special case of divergent evolution
species rapidly diverge into many new species over extremely short time
offspring resemble founder individual
genetic drift
gene pool changes erratically & rapidly
species have little/no competition or stress
ex: Galapagos & Hawaiian Islands
free from herbivores
gene flow does not keep the species homogeneous throughout its entire range
reproductively isolated
alleles arise in one part in range and don't reach others in other parts
abiological & biological reproductive barriers
process by which natural selection caused new species to evolve
distinct species
two organisms do not produce fertile offspring when crossed
some populations of species evolve into a new second species
others remain unchanged as original parental species
evolve into new third species
Convergent Evolution
two, distinct unrelated species occupy the same or similar habitats
natural selection may favor same phenotypes in each
only phenotypes converge not geneotypes
two may evolve to a point where they resemble each other strongly
ex: cacti & euphorbias
Evolution and the Origin of Life
Conditions on Earth Before the Origin of Life
Chemicals Present in the Atmosphere
earth initially hot and rocky
condensed from gases & dusts
composed mostly of hydrogen
light gas
first atmosphere lost in space
replaced by second atmosphere
was a reducing atmosphere
lack of molecular power
presence of powerful reducing agents
Energy Sources
powerful sources of energy
UV & gamma radiation from sun
highly reactive free radicals
chemicals
ammonia decomposed
nitrogen
hydrogen
methane converted
carbon monoxide
carbon dioxide
heat
coalescence of gas and dust
form earth
kinetic energy to heat
radioactive decay
keeps earths core molten
electricity
abundant
rainstorms last thousands of years
generating tremendous amount of lightning
triggered chemical reactions
resulting products washed downward by rain
volcanoes
produced lightning around throats
venting gases in clouds
hydrogen sulfide
methane
ammonia
water
Time Available for the Origin of Life
Chemical Produced Chemosynthetically
test of chemosynthetic hypothesis
performed by S.Miller
constructed container
boiling water in bottom
reducing atmosphere in top
electrodes discharged sparks into gases
stimulating lightning
solution was dark
organic compounds formed
plausible model
Formation of Polymers
monomers present in early ocean had to polymerize if life to arise
required high concentrations of monomers
formation of seaside pools @ high tide
evaporate after tide goes out
sunlight warm pools
polymerization reactions could occur
could accumulate in icy ponds/pools
ice relatively pure
monomers concentrated in not yet frozen water
produce class polymers distinct from high temps
absorption of clay
clay tiny fragments of rocks regular crystalline surface
organic molecules adhere to them in particular orientation
similar to binding to enzyme
primitive catalysts
Aggregation and Organization
aggregation of chemical components into masses
some organization
some metabolism
fatty, hydrophobic material accumulated automatically
as oil slicks in quiet water
droplets in agitated water
fatty acids occupy outermost layer
accompined by molecules
proteins
first aggregates formed @ random
not postulated to have been alive
Early Metabolism
aggregates
complete heterotrophs
absorb all material from ocean
modify only few molecules
consume certain nutrients
scarcity occurred
synthesize scare molecule from abundant one in ocean
metabolic pathway
two steps long
invoves two enzymes
advantage over others
more rapid metabolism
grown & reproduce more rapidly
abundance increased
scarcity occured again
natural selection
Oxygen
evolution of chlorophyll a & photosynthesis that liberated O2 has profound consequences
allowed world to rust
created conditions that selected for evolution of aerobic respiration
chlorophyll a evoleved
raw material for photosynthesis
water
free O2 released as waste
atmosphere present today derived from early second atmosphere
oxidizing atmosphere
build up of atmospheric oxygen has important affects
under influence UV light, oxygen transformed into ozone
The Presence of Life
chemistry of living creatures is more complex than that of nonliving objects
no unique properties
important to understand processes in their complexity
physics of living and nonliving world identical
chemosynthesis
4 conditions neccesary
1.) the right inorganic chemicals
2.) appropriate energy sources
3.) great deal of time
4.) absence of oxygen in its destructive molecular form, O2
