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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Population Genetics
Changes in prevalence of alleles over time
Factors that Cause the Gene Pool to Change
Mutation
Existing alleles decrease in frequency
New alleles increase in frequency
Only method to introduce a new allele into a population, besides inter-population breeding
Accidents
Events to which an organism cannot adapt
Allele frequencies within impact zone are eliminated
Bottle-necking effect
Examples
Volcanic Eruption
Floods
Droughts
Hailstorms
Artificial Selection
Humans purposefully change allele frequency of a gene pool
Often carried out in conjunction with artificial mutation
Selective breeding of crop plants, domestic animals, etc.
Natural Selection
The most significant factor causing gene pool changes
"Survival of the fittest"
Two conditions must be met
More offspring than can survive to maturity
Progeny must differ from each other in their allele types
Factors that Are Not Part of Natural Selection
Purpose
Intention
Planning
Voluntary decision making
Multiple Selection Pressures
Alleles which may be selectively advantageous for one Selection Pressure, can be wiped out by a different pressure
Complicates things, difficult to calculate
Speciation
Natural selection causes a new species to evolve
Can occur in 2 fundamental ways
Phlyetic speciation
New beneficial alleles are selected for and spread throughout the population
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Gene Flow
Pollen Transfer
Seed Dispersal
Vegetative Propagation
Divergent Speciation
If gene flow is not homogeneous
Reproductive isolation
Abiological reproductive barrier
Results in
Allopatric/geographic speciation
Physical and topographical barriers
Biological Reproductive Barriers
Any biological phenomenon that prevents successful gene flow
Sympatric speciation
Prezygotic isolation mechanisms
Postzygotic internal isolation barriers
Hybrid sterility
Hybrid inviability
Adaptive Radiation
Species rapidly diverges into many new species over an extremely short period of time
Examples: Hawaiian and Galapagos Islands
All offspring greatly resemble the founder individuals
Genetic drift is the erratic change in a gene pool caused by accidents or disasters
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Convergent evolution
Two distinct, unrelated phenotypes occupy the same/similar habitats
Evolution to the point that the species closely resemble each other
Evolutionary convergence of cacti and euphorbias
https://www.khanacademy.org/science/biology/her/tree-of-life/v/allopatric-and-sympatric-speciation
Evolution and the Origin of Life
Conditions on Earth Before the Origin of Life
Chemicals Present in the Atmosphere
First atmosphere was mostly hydrogen
Second atmosphere
H2S
NH3
CH4
H2O
Reducing atmosphere due to the lack of Molecular oxygen and presence of powerful reducing agents
Energy Sources
Intense UV and Gamma radiation
Heat
Electricity
Volcanic lightning
Time Available for the Origin of Life
Chemosynthetic origin of life basically had no time limit
Oceans= primordial soup
Due to lack of molecular oxygen as oxidizing agent to breakdown primodial compounds
Chemicals Produced Chemosynthetically
First experimental tests of the chemosynthetic hypothesis performed in 1953 by S. Miller
University
of CHicago
All of the necessary materials for life can be produced by recreating a microcosm of the circumstances of the primordial secondary atmosphere
Formation of Polymers
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Polymerization could have occurred via numerous mechanisms; Tide pools, absorption by clay particles, naturally over time, etc.
Aggregation and Organization
The first aggregates would have formed stochastically, controlled only by relative solubility
At some point an aggregate formed that had heritable information molecules able to direct the synthesis of products useful to the product
