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Population Genetics and Evolution, biology-form-5-chapter-4-45…
Population Genetics and Evolution
Concepts
evolution
conversion of one species into one or more types of new species
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natural selection
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slow process, takes years
Population Genetics
deals with the abundance of different alleles in a population
crossing over
total number of alleles in all the sex cells
gene pool
sexual reproduction does not change gene pool
other factors change gene pool
factors that cause gene pool to change
accidents
organism cannot adapt
meteorites and volcanic eruptions ect.
could be big or small
mutations
depends on population size
existence of even a single copy should not be ignored
occur continually
Artificial selection
humans purposely change the allele frequency in a gene pool
breeding crops and domestic animals
conjunction with artificial mutation
desired phenotypic plants used in selective breeding
Natural selection
most significant factor causing gene pool changes
survival of the fittest
population must produce more offspring that can grow and survive to maturity in that habitat
progeny must differ from each other in their types of alleles
act on only preexisting alleles
Factors that are not part of natural selection
natural selection does not include
intention
planning
purpose
voluntary decision making
Situations in which natural selection does not operate
cant operate if all individuals of a population are identical genetically
impossible to become adapted to certain conditions
survival is universal= no natural selection
multiple selection pressures
loss of individuals and reduced reproduction
not single factor
Rates of Evolution
allelic combinations don't always change rapidly
few mutations produce a phenotype so superior that it immediately changes something
Speciation
natural selection causes a new species to evolve
do not produce fertile offspring if crossed means two different species
freely interbreed in nature= same species
occurs in 2 ways
phyletic speciation
changes so much becomes new species
divergent speciation
some populations become new species while others continue unchanged
phyletic speciation
gene flow
movement of alleles physically through space
pollen transfer
each carry one full haploid genome
wind distributed
animal- mediated pollination also contributes
allele movement can be rapid
seed dispersal
some seeds of plants fall close by them
seeds can be carried by wind, floods, and stream flow
vegetative propagation
species produces small, mobile pieces the reproduce vegetatively
alleles that arise at different sites, come together by gene flow
Divergent Speciation
reproductive isolation
abiological reproductive barriers
speciation is called allopatric or geographic speciation
mountains are reproductive barriers
biological reproductive barrier
a biological phenomenon that prevents successful gene flow
sympatric speciation
two groups become reproductively isolated even though they grow together
changes in pollinators can also act as reproductive barriers
prezygotic isolation mechanisms
before zygote can be formed
postzygotic internal isolation barriers
two subpopulations must be considered separate species
hybrid sterility
two populations occasionally interbreed artificially cross-pollinated and produce viable seeds but plant is sterile
hybrid inviability
embryo or zygote dies early in development
Adaptive Radiation
special case of divergent evolution in which a species rapidly diverges into many new species short time
founder individuals
founder
original gene pool consists of its two set of alleles
genetic drift
gene pool can change rapidly and erratically
Convergent evolution
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two may evolve to the point that they resemble each other strongly
two groups cannot converge to the point of producing same species, only phenotypes converge
Evolution and the Origin of Life
chemosynthesis
rejects divine intervention
A. Oparin, 1924
right inorganic chemicals, appropriate energy sources, lots of time, and no oxygen
conditions on earth before life
chemicals in atmosphere
first atmosphere hydrogen
second atmosphere: hydrogen sulfide, ammonia, methane, and water
reducing atmosphere: lack of oxygen
Energy sources
intense gamma and UV radiation
heat
kinetic energy
radioactive decay
electricity was abundant
volcanoes producing lightening
Time available for the origin of life
no limits, cause of lack of molecular oxygen
no oxygen so no breaking down of chemicals being created
Chemicals produced chemosynthetically
all molecules essential for life can be formed this way
formation of polymers
clays may have both concentrated monomers and acted as first primitive catalysts
Aggregation and Organization
chemical components into masses
first ones formed randomly
eventually had RNA
Early Metabolism
aggregates would have been complete heterotrophs
absorbing all material from the ocean
glycolysis evolved early
Oxygen
two consequences
evolution of aerobic respiration
allowed world to rust
free oxygen very low
oxidizing atmosphere
ozone
presence of life
complex
Natural selection is a factor that causes a change in the gene pool
Convergent Evolution takes awhile to complete
There are many different way species are determined
