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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Population Genetics
Factors causing Gene Pool to Change
Mutation
occur continually
all genomes are subject to mutagenic factors
Accidents
events to which organisms can't adapt
phenomena
can be small events, as well as large
Artificial Selection
process by which humans purposefully change the allele frequency of a gene pool
used to produce ornamental plants that flower more abundantly
or for a longer time
crop plants and domestic animals
rice, wheat, and corn
Natural Selection
#
most significant factor causing gene pool changes
survival of the fittest
differential survival among organisms that have different phenotypes
Factors that Are Not Part of Natural Selection
does not include:
purpose
intnetion
planning
voluntary decision making
Multiple Selection Pressures
loss of individuals and reduced reproduction
not always caused by a single factor
Situations in which Natural Selection Does Not Operate
when individuals of a population are identical genetically
or if it is impossible to become adapted to a certain condition
if survival is universal
definition:
deals w abundance of different alleles within population
gene pool
total # of alleles in all sex cells of all individuals of a population
Rates of Evolution
allelic composition of a population do not change rapidly
most populations are well adapted to their habitat
or they would not exist
evolutionary changes that result in the loss of a structure or metabolism
can come about quickly
complexity
Speciation
Convergent Evolution
unrelated species that occupy the same or similar habitats
then the 2 may evolve so that they resemble each other
so that natural selection does not kill off one
definition:
natural selection that has caused a new species to evolve
speciation can occur in 2 fundamental ways
phyletic speciation
one species gradually becomes so changed it must be considered a new species
divergent speciation
some populations of a species evolve into a new, second species
while other populations either continue relatively unchanged
the original species evolved unto a new third species
phyletic speciation
#
gene flow
movement of alleles physically through space
occurs in many ways:
pollen transfer
allele movement can be rapid
animal-mediated pollenation
seed dispersal
seeds can fall close to the parent
many species have long-distance dispersal mechanisms
can be carried by wind, floods, and stream flow
seeds/fruits that are spiny & gummy can stick to the fur of animals
vegetative propagation
small mobile pieces that reproduce vegetatively
can contribute to gene flow
divergent speciation
#
reproductively isolated
abiological reproductive barriers
any physical, nonliving feature that prevents 2 populations from exchanging genes
allopatric
if speciation occurs
biological reproductive barriers
any biological phenomenon that prevents successful gene flow
sympatric speciation
when 2 groups become reproductively isolated even though they grow together
prezygotic isolation mechanisms
biological reproductive barriers that prevent pollination and fertilization
hybrid sterility
earliest postzygotic barriers
Evolution and the Origin of Life
Aggregation and Organisms
aggregation of chemical components into masses
have some organization and metabolism
aggregates would have formed at random
Early Metabolism
glycolysis must have evolved early
would have been a metabolic pathway 2 steps long involving 2 enzymes
Formation of Polymers
intense sunlight heated pools and polymerization reactions could occur
clays might have both concentrated monomers
acted as the first primitive catalyst
Oxygen
allowed the world to rust
created conditions that selected for evolution of aerobic resp.
oxidizing atmosphere
derived from early second atmosphere
by the addition of oxygen from photosynthesis
The Presence of Life
gradual transitions from completely inorganic compounds
to living bacteria
Conditions on Earth Before the Origin of Life
Energy Sources
intense UV & gamma radiation from sun
these have energetic quanta
heat was another source
Time Available for the Origin of Life
no limits
1.1 billion years may have passed between when earth solidified and life arose
Chemicals Present in the Atmosphere
second atmosphere
produced by release of gases from the rock matrix
and from heavy bombardment by meteorites
early second atmosphere was a reducing atmosphere
lack of molecular oxygen
and powerful r3educing agents