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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Concepts
Evolution
Gradual conversion of one species to another over time
Occurs by natural selection
Mutations that affect an individuals fitness
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Extremely slow process
Theory created by Darwin and Wallace
Population Genetics
The abundance of different alleles in a population
And how an allele abundance changes over time
Gene pool
The total number of alleles in the sex cells
Factors that cause the gene pool to change
Mutation
Accidents
Events where an organism cannot adapt
The organisms die and their alleles are lost
Many phenomena qualify as accidents
Volcanic eruption, floods, hailstorms, drought
Can be small or large phenomena
Artificial selection
Process which humans change allele frequency
In conjunction with artificial mutation
Acridine dyes, UV, and Gamma rays try to increase new alleles
Natural Selection
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Two conditions must be met before occuring
Population must produce more offspring
Able to grow and mature
Affected by resources, predators, pathogens, and competitors
Progeny must differ from each other in allele types
If all is identical, no mutations can occur
Genetic diversity allows for different survival
Does not always occur from outside sources
Factors not part of natural selection
Purpose
Intention
Planning
Voluntary decision making
Situations which Natural Selection Does Not Operate
When a population is identical
Universal survival
Multiple Selection Pressures
Reduced reproduction is not caused by a single factor
New, useful alleles can still be lost
If the plant dies from lack of a certain allele
Ex: cold resistant allele is lost due to fungus killing the plant
Rates of Evolution
Most populations are well adapted to their environment
Some alleles are hard to identify
Unless shown in phenotype
Speciation
The process of a species evolving
Can occur in two different ways
Phyletic speciation
A species becomes a new different species
Often Requires millions of years
The movement of alleles is called gene flow
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Pollen transfer
Pollen carries a full haploid genome
Can be transferred by wind or animals
Rapid movement
Seed Dispersal
Spreads by wind and animal
Vegetative propagation
Species reproduce by small mobile vegetative pieces
Divergent speciation
Populations evolve into a second species
New gene ranges arise from not being homogenous
The new and old ranges are reproductively isolated
Abiological reproductive barriers
Nonliving feature that prevents gene exchange
Can cause allopatric or geographic speciation
Ex: Mountains, deserts, oceans
Biological reproductive barriers
Any biological phenomena that prevents gene flow
Sympatric speciation
When two groups grow together, but are reproductively isolated
Evolutionary changes in pollinators
Called prezygotic isolation mechanisms
Act before zygotes form
Postzygotic internal isolation barriers
When alleles get too distinct and cannot interbreed
Hybrid sterility can cause plants to not reproduce
Hybrid inviablity is when a plant dies at an early age
Adaptive radiation
Special case where species rapidly diverge
Usually happens when species have no competition
All offspring resemble founder individual(s)
The seed (founder) where the gene pool started
Genetic drift
Gene pool changes rapidly and erratically
Convergent evolution
When two species strongly resemble each other
Two species cannot become one
Evolution and the Origin of Life
Chemosynthesis
Hypothesis that models the origin of life with known processes
Chemical and physical processes
4 conditions for chemosynthetic origins
Correct inorganic chemicals
Appropriate energy sources
Great deal of time
Absence of oxygen, O2
Conditions on Earth before the origin of life
Chemicals present in the atmosphere
First atmosphere was lost
Hydrogen is a light gas
Second atmosphere replaced first
Reducing atmosphere
Energy sources
Intense UV and gamma radiation
Heat
The coalescence of gas and dust
Radioactive decay of heavy elements
Electricity was abundant
Triggered chemical reactions in the atmosphere
Volcanoes produce lightning
Time available
Had no limits for chemosynthetic origins
Due to lack of oxygen
Chemicals produced chemosynthetically
First experiment of chemosynthesis done by S. Miller (1953)
Experiments tell us what is theoretically possible
Formation of polymers
Monomers in early oceans polymerized
Oceans went from diluted to concentrated
Absorption from clay concentrated monomers
Could have been the first primitive catalysts
Aggregation and organization
First aggregates formed randomly
Controlled by relative solubility
Would have simple "metabolism"
Not alive due to lack of genetic information
At some point heritable information was obtained
Helped aggregate grow and reproduce
Early metabolism
Aggregates were complete heterotrophs
Metabolic aggregates increased
A second chemical process could form chemosynthetically
Energy metabolism
Glycolysis evolved early
Cellular respiration processes would form after
Oxygen
Photosynthesis had two consequences
Would allow the world to rust
Created aerobic respiration
Was released into the atmosphere
Created an oxidizing atmosphere
Organisms that could detoxify oxygen had selective advantage
The presence of life
When can we say life began?
Can aggregates be considered alive?
Difficult questions to answer
No demarcation between living and nonliving objects
