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Population Genetics and Evolution (Evolution and the Origin of Life (Time…
Population Genetics and Evolution
Population Genetics
The abundance of different alleles within a population
Abundance of increase, decrease and remaining the same
Crossing over increases genetic diversity
Gene pool
Total number of alleles in all the sex cells
Factors that Cause the Gene Pool to Change
Mutation
Mutations occur continually
All genomes are subject to mutagenic factors
Existing alleles decrease
New alleles increase
Accidents
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Events an organism cannot adapt
Such as a meteorite colliding with Earth
Volcanic eruption
Infrequent floods, drought, hail storms
Artificial Selection
Humans purposefully change allele frequency in gene pool
Selective breeding of crop plants
Domestic animals
Choose the ones who have desirable qualities
Used to produce ornamental plants
Artificial mutation
Increase the number of new alleles
Natural Selection
Most significant in gene pool changes
Survival of the fittest
Two factors must be met before occurring:
Population must produce more offspring
Able to survive to maturity
Progeny must differ from each other
In their types of alleles
Differential survival among organisms
Have different phenotypes
Factors that Are Not Part of Natural Selection
Purpose
Intention
Planning
Voluntary decision making
Rates of Evolution
Allele composition does not change rapidly
Very few mutations create new phenotypes
Many seedless plants
Million of years without diverging
Lyopods, Equisetum, ferns
Most studies of evolution concern changes in:
Shoot
Flowers
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Fruits
Roots
Leaves
Trichomes
Most mutations become advantageous
Speciation
Natural selection causing a new species
Two functional ways:
Phyletic speciation
One species gradually changes into new
Divergent speciation
Evolve into new, second species
Phyletic Speciation
Millions of years are often required
For a new species to evolve into a new one
New beneficial alleles spread
Movement of alleles physically through space
Gene flow
Pollen transfer
Pollen grains
Carry one full haploid genome
All alleles are present
Wind distribution
Spread pollen long distances
Birds and insects
Spread pollen short distances
Seed dispersal
Long-distance dispersal mechanisms
Can be carried by:
Wind
Floods
Stream flow
Birds carry and forget about them
Vegetative propagation
Species produce small, mobile pieces
Reproduce vegetativley
Divergent Speciation
Does not keep homogeneous throughout
Reproductively isolated
Alleles that arise in one part of range
But not the other part
Two fundamental causes:
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Abological reproductive barriers
Physical, nonliving feature
Prevents two populations from exchanging genes
Original species physically divided
Into two or more populations
Cannot interbreed
Allopatric
Genographic speciation
Biological reproductive barriers
Phenomenon that prevents gene flow
Differences in:
Flower color
Flower shape
Flower smell
Two groups become reproductively isolated
Even though they grow together
Sympatirc speciation
Evolutionary changes in pollinators
Prevent pollen from moving
Pollination nor fertilization occur
Prezygotic isolation mechanisms
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Postzygotic internal isolation barriers
Two sub-populations considered seperate
Hybrid sterility
Two populations occasionally interbreed
Artificially cross-pollinated
Produce viable seed
Seed grows into a sterile plant
Hybrid inviability
Sterile hybrid cannot result
Zygote or embryo dies early in development
Adaptive Radiation
Special case of divergent evolution
Species rapidly diverge into many new species
In only a few million years
Founder individuals
Offspring resemble
Initial gene pool is extremely small
Founder
Original gene pool consists of its two sets of alleles
Genetic drift
Gene pool can change rapidly and erratically
More subject to accidents
Convergent Evolution
Two distinct, unrelated species occupy the same habitat
Natural selection favors both phenotypes
Two may evolve and resemble each strongly
Evolution and the Origin of Life
Most seriously considered hypothesis
Chemosynthesis
Using only known chemical and physical processes
Conditions on Earth Before the Origin of Life
Chemicals present in the atmosphere
Second atmosphere
Produced by release from gases
Reducing atmosphere
Due to lack of molecular oxygen
Presence of powerful reducing agents
Energy source
Intense UV and gamma radiation
Time available for the Origin of Life
Ocean was called "dilute soup"
Containing water, salts and organic compounds
Had no limits
1.1 billion years before life arose
Formation of Polymers
Oxygen
Evolution of chlorophyll a and photosynthesis
It allowed the world to rust
Evolution of aerobic respiration
Oxidizing atmosphere
