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Chapter 17: Population Genetics and Evolution (Population Genetics…
Chapter 17: Population Genetics and Evolution
Concept
evolution
gradual conversion of one species
into one
in some cases
several new speies
extremely slow process require thousands of generations
millions of years produce obvious change in species
most part by natural selection
mutations cause new alleles
new genes to arise affect fitness of individual
making it less or more adapted to environment than other without allele or gene
Population Genetics
Factors that Cause the Gene Pool to Change
mutation
all genomes are subjected to mutagenic factors
mutation occur continually
existing alleles decrease in frequency
new alleles increase
accidents
organism cannot adapt
collision of large meteorite with earth
many phenomena qualify
artificial selection
humans purposefully change allele frequency of gene pool
example
selective breeding of crop plants
domestic animals
natural selection
most significant factor causing gene pool changes
usually described as survival of the fittest
individuals are most adapted to environment survive
less adapted do not
important factor in evolution that must be given careful attention
factors that are not plant of natural selection
understood more clearly
accurately if the certain factors not part of natural selection
purpose
intention
planning
voluntary decision making
Situations in which Natural Selection Does Not Operate
gained by considering several cases in does not operate
abundance of different allele within population
manner in which abundance of particular allele
increases
decreases
remains the same with time
population concept of species
similar ranges of variation occur in all species
true of plant
type concept of species
later 1800s
base on types
gene pool
total # of allele in sex cells individuals
Multiple Selection Pressures
loss of individuals
reduced reproduction not caused by single factor
such as pathogenic fungus
Rates of Evolution
allelic composition of population could change rapidly
not typically the case
many species of seedless plants
lycopods
equisetum
ferns
very rapid speciation occur in group of aster in Hawaii
shortly after Kauai formed 5.2 million years ago
aster seed arrived
thrived
reproduced
spread rapidly in unpopulated island
Speciation
Phyletic Speciation
two fundamental
phyletic speciation
species gradually becomes changes must be considered new species
divergent speciation
#
million of years often required for a species to evolve into new species
pollen transfer
each carry one full haploid genome
all alleles of plant are present in pollen grains
seed dispersal
some plant fall close to the parent
many species have long-distance dispersal mechanisms
vegetative propagation
small
mobile species reproduce vegetatively
too contribute to gene flow
Divergent Speciation
reproductively isolated
divergent speciation may occur
if alleles arise in one part of the range o not reach individuals in other
two fundamental
abiological
biological reproductive barriers
abiological reproductive barrier
any physical
nonliving feature prevents two populations from exchange gene
allopatric
geographic speciation
original species physically divided into two or more population cannot interbreed
speciation results
biological reproductive barriers
any biological phenomenon prevent successful gene flow
sympatric speciation
two group become reproductively
isolated even though then grow together
prezygotic isolation mechanisms
act even before zygote can be formed
adaptive radiation
special case divergent evolution in species rapidly diverges into many species over an extremely short time
few million years
Convergent Evolution
two evolve to the point that resemble each other strongly
have undergone
speciation
natural selection has new species to evolve
Evolution and the Origin of Life
Conditions on Earth Before the Origin of Life
second atmosphere
hydrogen such a light gas
most of first atmosphere was lost into space
reducing atmosphere
due to lack of molecular oxygen
presence of powerful reducing agents
time available for the origin of life
chemosynthetic origin of life basically no limits
Chemicals Produced Chemosynthetically
direct analysis of meteorites
lunar samples reveals in nonliving environments
Formation of Polymers
early ocean have polymerize if life were arise
polymerization required high concentration of monomers
Aggregation and Organization
first aggregate
basically at random
controlled only by relative solubility
Early MEtabolism
complete heterotrophs
absorb all material from ocean
modifying only a few molecules
Oxygen
two profound consequences
allowed the world rust
created conditions that selected for evolution of aerobic respiration
The presence of Life
chemosynthetic theory postulated a long series for slow
transitions from completely inorganic compound to living bacteria
