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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
Mutation
All genomes subject to mutagenic factors
Existing alleles decrease in frequency
new alleles increase
Accidents
Events where an organism cannot adapt
meteor strikes earth
Eliminates large amount of population
Eliminates population alleles
examples
volcanic eruption
floods hailstorms droughts
droughts
affects plants that need water
may not affect plants that don't
Can be small and large
Artificial Selection
When humans purposefully change allele frequency
plant breeders
search for desirable qualities for crops
plants with desirable qualities' seeds used in future
gene pool for most crops today have been artificially selected over thousands of years
Natural Selection
most significant factor
"survival of the fittest"
individuals most adapted to environment survive
two conditions must be met
must produce more more offspring that can grow
plants produce 100s of seeds
most seeds do not travel far
Herbivorous animals
eat plants
may rob nectar without pollinating
progeny must differ in allele types
if they were identical
affected by adversity the same
equally susceptible to pathogenic fungi
no change in allele frequency
diversity
pathogenic fungi attack
member with resistant alleles survive
surviving members breed and a resistant population is formed
plants with advantageous traits grow faster
will produce more seeds
at least half of the new seeds will have good trait
Natural selection only works if it kills individuals
factors not part of natural selection
purpose, intention, planning, voluntary decision making
plants cannot plan activities and have purpose
contain certain alleles due to survival of ancestors
ancestors with good traits survived
these events not planned
ancestors with weak traits died off
along with alleles for weak traits
Situations in which Natural selection does not operate
cannot operate if a population is genetically identical
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if it is impossible to adapt to a certain condition
if survival is universal
Multiple Selection Pressures
loss of individuals not caused by 1 factors
alleles for some good traits may be killed off
plant could be killed by fungus, which it doesn't protect against
Abundance of different alleles in a population
manner than they increase decrease of stay the same
Rates of evolution
most populations are well adapted to environment
hard to identify alleles that dont affect phenotype
disruptive mutations outnumber constructive ones
changes that result in structure, metabolism change
occur quickly
occur complexly
Speciation
Phyletic Speciation
enough changes it is a new species
requires millions of years
gene flow
movement of alleles physically
occurs by
pollen transfer
pollen grains carry one haploid genome
all alleles of a plant are present
distribution
wind carries pollen far
animal-mediated
usually causes pollen to stay in a small area
causes genes to stay close
seed dispersal
fruits/seeds of some plants fall close to parent
many species have long distance dispersal
carried by wind, floods, and stream mechanisms
sticky seeds can stick to bird wings
vegetative propagation
some plants produce small, mobile pieces
Divergent Speciation
populations evolve into new second species
other populations stay the same
some populations evolve into third species
Abiological Reproductive Barriers
physical, nonliving feature that prevents gene exchange
Mountain ranges are common of this
pollinators do not fly across ranges
seeds that are carried across are rare
plants on top of a mountain often isolated
original species divided into two populations
they cannot interbreed
if speciation results it is allopatric
Convergent Evolution
unrelated species in same habitat
natural selection could favor same phenotypes
could evolve so that they look alike
same phenotypes does not mean same genotype
may look alike but can not interbreed
have different ancestor plants
when natural selection creates new species
Biological reproductive barriers
biological phenomenon that prevents gene flow
flower shape, color, and fragence
can prevent gene flow
pollinators are biased to certain traits
If a plant doesnt get pollinated its alleles are eliminated
timing
flowers open in the morning
flowers open in the evening
do not interbreed
Evolutionary barriers
plants over a large area
different characteristics
elevation
temperature
humidity
may not matter to plant
often matter to pollinators and seed distributors
prezygotic isolation mechanisms
act before zygote can form
postzygotic internal isolation barriers
evolutionary barriers have created subspecies
create new genomes
genomes become too different to breed together
hybrid sterility
two populations interbreed and create viable seed
the seed grow into a sterile plant
no synapsis
homolgous chromosomes no longer homologous
1 more item...
subpopulations of plants emerge from interbreeding
subpopulations develop new alleles
Adaptive Radiation
special case of divergent evolution
species changes in short period of time
occurs when there is no competition/environmental stress
all offspring greatly resemble first
gene pool small
more subject to accidents
can cause gene pool to change rapidly
if one seed is founder, gene pool only two alleles
evolution and the origin of life
Conditions on Earth Before the Origin of Life
Chemicals present in the atmosphere
earth condensed from gases and dust 4.6 million years ago
mostly H at first
second atmosphere formed
H2S, NH3, CH4 and H20
energy sources
complex chemistry in early second atmosohere
exposed to intense UV and gamma radiation
these radiations knock electrons from atoms
NH3 would have decomposed
Heat was available to power reactions
rain was persistent
evaporated when it touched hot earth
rain would have lasted 1000s of years
lightning strikes powered reactions
Time available
no limits for life
oxygen was not present to break down chemicals
ocean contained many organic compounds
Chemicals produced chemosynthetically
experiments done to test chemsynthetic hypothesis
water boiled
electrodes sparked
organic acids formed
amino acids
lipids
nitrogen bases
Formation of polymers
monomers had to polymerize if life were to come
oceans would have become concentrated
pools form at seaside
these pools would contain monpmers
Aggregation and Organization
chemical components aggregated into masses
hydrophobic material would have accumulated
fatty acids occupied outmost layers
first aggregates would have formed at random
heterotrophs
countless aggregates would have formed
would have dissociated
Early metabolism
complete heterotrophs
aggregates continued to consume certain nutients
natural selection
favored anything that could advance metabolism
aggregates would have absorbed some atp
Oxygen
allowed rust
without iron oxygen might have killed everything
created conditions for aerobic respiration
chlorophyll a evolved
occurred 2.8 billion years ago
created an oxidizing atmosphere
The presence of life
chemosynthetic theory postulates long series of slow reactions
dont know when life came to be
a dividing line would be simplistic
