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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Population Genetics
Situations in which Natural Selection Does Not Operate
Cannot operate if all of a population are identical genetically
or, if it is impossible to become adapted to a certain condition
Multiple Selection Pressures
Some of the factors include:
Drought
Cold
Insect attack
Need for pollinators
Need for a mechanism to disperse their seeds
Pathogenic fungus
Reduced production is not caused by only a single factor
Factors that Cause the Gene Pool to Change
Artificial Selection
Process when humans purposefully change;
allele frequencies of a gene pool
Used to produce produced ornamental plants
these plants flower more often or for a longer time
Natural Selection
Most significant factor causing gene pool changes
described as survival of the fittest
Two conditions must be met for this to occur:
Population must produce more offspring than can grow & survive
to maturity in that habitat
Progeny must differ from each other int heir types of alleles
Accidents
When an organism cannot adapt
Many phenomena qualify as accidents
Other species that consist of plants with larger bodies
This acts as selective forces
Which removes weaker, less-adapted individuals
Does not affect the more well-adapted members
Factors that Are Not Part of Natural Selection
Intention
Planning
Purpose
Voluntary decision making
Mutation
Occurs continually
New alleles increase
Existing alleles decrease in frequency
Rates of Evolution
Allelic composition of a population could change rapidly
Most populations are well adapted to their habitat
Or else they would not exist
Typically it is difficult to identify the presence of particular alleles
Unless there is an easily identifiable effect on the phenotype
Speciation
Divergent Speciation
Biological reproductive barriers
Any biological phenomenon that prevents successful gene flow
There are differences in:
Color
Shape
Fragrance
Adaptive radiation
Special case of divergent evolution in which a species
Diverges into many new species over a short time
Abiological reproductive barriers
Any physical, nonliving feature that prevents
two populations from exchanging genes
Convergent Evolution
Two may evolve to where they resemble each other strongly
Two groups cannot converge to produce the same species
Only the phenotypes converge
Phyletic Speciation
Gene flow occurs in three ways:
Seed dispersal
Vegetative propagation
Pollen transfer
Gene flow:
Movement of alleles physically through space
Formation of new and distinct species in the course of evolution
Evolution and the Origin of Life
Aggregation and Organization
Chemical evolution of life would have been aggregation of chemical components
The 1st aggregates would have formed at random
Aggregates are not postulated to have been alive
An aggregate formed that did have a heritable information molecule
Which is able to direct the synthesis of products useful
Early Metabolism
As aggregates continued to consume certain nutrients
Any aggregate that could produce an enzyme capable of:
Synthesizing the scarce molecule from an abundant one
that may still be available
Formation of Polymers
Monomers had to polymerize if life were to arise
Polymerization required high concentrations of monomers
Obvious method of concentration
Is formation of seaside pools at high tide that evaporate
After the tide goes out
Chemicals Produced Chemosynthetically
Oxygen
Evolution of chlorophyll a & photosynthesis that liberates O2 had 2 consequences
It allowed the world to rust
It created conditions that selected for the evolution of aerobic respiration
Oxidizing atmosphere
Early second atmosphere by the addition of oxygen from photosynthesis
Conditions on Earth Before the Origin of Life
Energy Sources
Intense UV & gamma radiation from the sun
These radiations have energetic quanta
This energy knocks electrons from atoms
which creates highly reactive free radicals
Heat was another source of energy
Electricity was abundant on a big scale
Time Available for the Origin of Life
Basically has no limits
Because of the lack of free molecular oxygen
W/out oxygen
No agent was present to cause the:
Breakdown
Decomposition
Chemicals Present in the Atmosphere
Second Atmosphere
Release of gases from the rock matrix
Composing Earth and from heavy bombardment by meteorites
Reducing Atmosphere
Lack of molecular oxygen
& presence of powerful reducing agents
The Presence of Life
Chemosynthetic theory
Long series if slow, gradual transitions
From completely inorganic compounds to living bacteria
