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Chapter 17: Population Genetics and Evolution, Cross connection: Oxygen is…
Chapter 17: Population Genetics and Evolution
Concepts
Evolution
gradual conversion of one species into one or more species
Mostly occurs through natural selection
Mutation
Beneficial
Makes organisms more adapt
more likely to reproduce
Deleterious
Makes organism weaker
less likely to reproduce
Basis of natural selection discovered by
Charles Darwin
Alfred Russel Wallace
Occurs over a long period of time
Population Genetics
Factors that cause the gene pool to change
Mutations
All genomes subjected to mutagentic factors
occur continually
Existing alleles decrease
new alleles increase
Accidents
Events to which an organism cannot adapt
All organisms and alleles eliminated
Can be large or small events
Artificial Selection
Humans purposefully change allele frequency of a gene pool
used to produce
advantageous crops
ornamental plants
Different flower color and sizes
Lumber and paper trees
often used in conjunction with artificial mutation
Factors that are not part of natural selection
purpose
intention
planning
voluntary decision making
Natural Selection
#
most significant factor in gene pool changes
Survival of the fittest
More adapt individuals survive
Less adapt individuals die
Before it occurs, two conditions must be met
population must produce more offspring than can grow and survive to maturity
Progeny must differ from each other in types of alleles
differential survival among organisms with different phenotypes
Situations in which natural selection does not operate
individuals of a population are genetically identical
impossible to become adapt to certain condition
competition does not occur
Multiple selection pressures
Factors that pressure multiple factors of natural selection
the advantage of alleles may change as time passes
Definition
Deals with with abundace of different alleles within a population
manner in which an abundance of a particular allele changes over time
gene pool
total number of alleles of all individual in a population
Rates of Evolution
allele composition of population changes slowly
most populations already well adapt
Very few mutations produce new phenotypes
Some changes occur quickly
Some changes occur very slowly
Speciation
Phyletic speciation
gene flow
Movement of alleles physically through space
Occurs through
pollen transfer
pollen is distributed through
Wind
animals
can cause rapid alleles movement
seed dispersal
seed and fruit carried by
wind
flood
stream flow
rafting
sticking to animals
vegetative propagation
small mobile pieces that reproduce vegetatively
alleles the arise in one part of range travel to all parts
species remains relatively homogeneous
Divergent speciation
reproductive isolation
when allele in one part of range does not reach another part
causes
abiological reproductive barriers
any physical nonliving feature that prevents two populations from exchanging genes
if speciation is a result it is called
allopatric speciation
geographic speciation
biological reproductive barriers
#
any biological phenomenon that prevents successful hene flow
when two groups become reproductively isolated even while growing together the result is
sympatric speciation
biological barriers prevent pollen movement known as
prezygotic isolation mechanisms
when genomes become too different to interbreed known as
postzygotic internal isolation barriers
One of these barriers is hybrid sterility
One of the oldest of this type of barrier
hybrid is sterile
Hybrid inviability
hybrid dies early in development
two subpopulations are now considered different species
Adaptive Radiation
species rapidly diverges into many new species in a short time
occurs where
There is no or little competition
environmental stress exists
Founder individual
All offspring resemble this individual because gene pool is small
alleles build up in the population rapidly
Genetic drift
gene pool changes rapidly and erratically
Convergent evolution
Two species evolving to strongly resemble each other
two groups cannot converge to point of producing the same species
Natural Selection that has caused new species to evolve
Evolution and the Origin of Life
Conditions on Earth before the origin of life
Chemicals present in the atmosphere
Most of first atmosphere replaced by second atmosphere
produced by
release of gases from rock matrix composing Earth
heavy bombardment by meteorites
early second atmosphere was a reducing atmosphere
due to
lack of oxygen
presence of powerful reducing agents
Energy sources
complex chemistry in early second atmosphere
second atmosphere exposed to powerful sources of energy
foremost
intense UV
gamma radiation
Heat
source
coalescence of gas and dust
particles collide
radioactive decay of heavy elements
electricity
lightening from
rain storms
volcanoes
Allow for chemical reactions to occur
Time available for origin of life
no limit due to lack of free molecular oxygen
chemicals allowed to accumulate for millions of years
Chemicals produced chemosynthetically
sugars
amino acids
lipids
nitrogen bases
all other small molecules essential for life
Formation of polymers
High concentration of monomers needed
possible methods of concentration
Seaside pools
formed during high tide
evaporate when tide goes out
sunlight warms the pools
Clay absorption
molecules adhere in particular organization
crystalline matric of clay contains charges groups typically present in active sites of enzymes
Aggregation and organization
fatty hydrophobic acids
accumulated as
oil slicks in quiet water
droplets in agitated water
occupied outermost layer along with other molecules
inner layer may have been mostly hydrophobic
first aggregates
formed basically at random controlled only by relative solubility
would have had some simple metabolism
would have been heterotrophs completely
not postulated to have been alive
Early metabolism
aggregates with metabolic pathway two steps long involving two enzymes
ability to synthesize a scarce molecule from an abundant free one
advantageous
would have a mire rapid metabolism
energy metabolism
Oxygen
liberated through evolution of
chlorophyll a
photosynthesis
consequences
allowed world to rust
created conditions that selected for the evolution of aerobic respiration
accumulated in atmosphere to create an oxidizing atmosphere
created ozone which protects from UV light
The presence of life
#
difficult to say which stage life came to be
chemosynthetic theory delineates no absolute demarcation between living and nonliving objects
Chemosynthesis
hypothesis about origin of life on earth
attempts to model origin of life using only known chemical and physical processes
Cross connection: Oxygen is needed for biological processes
Cross Connection: Speciation is caused by natural selection
Cross Connection: Without the presence of life, population genetics would not exsist
