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Ch 17. Pop genetics, evolution (Evolution and the origin of life…
Ch 17. Pop genetics, evolution
Population Genetics
Alleles within a population
abundance+distribution
Changes in abundance
Sexual reproduction
2 different genotypes parents
increased genetic diversity
Same genotype in parents
No change in genetic diversity
Factors changing gene pool
mutations
decrease in existing allele frequency
one new mutation can become a large number of alleles
accidents
events to which an organism can't adapt
e.g. meteor strike
Can completely kill a specific allele
may cause no change to gene pool
depending on general population
artificial selection
humans changing allele frequency
E.g. crop breeding
to get most desirable qualities
continued use of artificial selection leads to large, permanent changes in gene pool
Natural selection
most significant factor
most adapted organisms survive+reproduce
offspring must outnumber ecological threshold
plants must have different alleles
e.g. fungus outbreak kills plants not fungal resistant
can't be purposely planned
Rates of evolution
typically takes more than a few generations
some plants hardly ever change
some plants change rapidly
mutations don't often change populations
Speciation
so much change in one species over time
leads to an entirely new species
a species
does not produce fertile offspring with another species
Phyletic speciation
one species gradually changes into a new one
requires millions of years
one beneficial allele must spread throughout the entire population
=gene flow
pollen transfer
pollen carries genomes and all alleles
may be spread by wind
ragweeds, grasses, conifers
may be spread by animals
insects
birds
seed dispersal
can be carried in different ways
wind
floods
stream flow
can stick to animals
vegetative propagation
divergent speciation
Reproductive isolation
alleles arising in one population cannot reach other populations
Abiological reproductive barriers
any physical, nonliving prevention of gene exchange
allopatric or geographic speciation
e.g. mountains
biological reproductive barriers
any biological phenomenon preventing gene flow
e.g. difference in flower color, shape, or fragrance
a different color flower may throw off pollinators
aka sympatric isolation
e.g. evolutionary changes in pollinators
prezygotic isolation mechanisms
prevent pollen flow, thus a zygote is never even formed
post zygotic internal isolation barriers
continued evolution of different subspecies
prevents breeding between the subspecies
hybrid sterility
2 subspecies interbreed
producing a sterile plant
certain populations of a species evolve into a new species
adaptive radiation
a species rapidly diverges into over an extremely short period of time
usually occurs when a species enters a new habitat
e.g. new hawaiian islands
founder individuals
first parents in new territory
lack of competition and outside threats
allows great diversification
called genetic drift
may occur in mainlands
if dominant species is wiped out
convergent evolution
two unrelated species follow the same evolutionary path
same phenotypes favored
Evolution and the origin of life
chemosynthesis
uses known chemical and physical processes
rejects divine intervention
suggests the pre-life earth chemical could react spontaneously
forming complex chemicals
complex chemicals continue to react
give rise to life maintaining chemicals
give rise to primitive protocells
would require 4 conditions
1) the right inorganic chemicals
2) appropriate energy sources
3) lots of time
4) an absence of molecular oxygen
produces chemicals
leads to production of
amino acids
sugars
lipids
nitrogen bases
earth conditions pre-life
Chemicals present
second atmosphere
produced from rock matrix composing earth
hydrogen sulfide
ammonia
methane
water
reducing atmosphere
due to
lack of molecular oxygen
presence of reducing agents
energy sources
sun
intense UV and gamma
knocks electrons
forming powerful free radicals
heat
coalescence of gas and dust
radioactive decay of heavy elements
electricity
lightning
due to
tremendous rainstorms
volcanic eruptions
time available
basically infinite
no molecular oxygen=no chemical decomposition
polymers
produced in
hot oceans
ice
due to high monomer concentration
aggregation
chemicals forming into masses
basically formed at random
leads to organization
leads to metabolism
due to enzymes
first enzyme producers would have an evolutionary advantage
oxygen
current atmosphere produced from early second atmosphere
all free iron on earth had to be oxidized first
a long period of rusting
an oxidizing atmosphere
life
evolved from nonliving compounds
when?