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Population Genetics and Evolution (Rates of Evolution (It is difficult to…
Population Genetics and Evolution
Population Genetics
Situations
Competition doesn't occur in a system that supports life of all individuals.
In these environments, natural selection does not occur.
Potential zones
Recently burned area
Recently flooded area
Sides of a road cut
Pressures
A mutation allele that is advantageous to resisting these pressures may not take hold, and could be eliminated by another factor.
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Mutative responses to pressures are often geared strictly to one pressure, whereas the opposite type of pressure will kill it quickly.
In most cases, loss of individuals isn't caused from one factor. but several.
Factors
Accidents
Events to which an organism cannot adapt, such as a volcanic eruption, fire, or cataclysmic events like a large meteor striking the planet.
There is a massive amount of phenomena that qualifies as an accident, large and small.
Genetic effects
Wipes out alleles of species in the area affected by accidents.
Other species near the area may be affected by contaminants spread by these events.
Selection
Artificial
Process where humans have an input on changes in allele frequency in species.
Useful for helping useful plants to breed.
Farming crops that are resistant to diseases and helping those to survive allows for more bountiful harvests.
Artificial selection may also be used for ornamental plants that flower more abundantly for longer periods.
Natural
Often referred to as "survival of the fittest".
Can only act on preexisting alleles.
Most significant factor causing gene pool changes.
Does not always result from action of an agent outside the organism.
Mutation
All genomes are subjected to mutagenic factors.
Even one mutagenic gene can have major effects on evolution of a species.
Because of mutation, existing alleles decrease in frequency, and new alleles increase
The entire system of evolution is driven, in large part, due to mutation.
Speciation
Divergent
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Biological Barriers
When 2 groups become reproductively isolated even though they grow together, the result is sympiatric speciation.
Evolutionary changes in reproductive carriers can become a barrier.
Biological phenomena that prevents gene flow is a biological barrier.
Environmental diversity of a large geographic range can lead to divergence between plants themselves.
Abiological Barriers
If speciation results, it is called allopatric or geographic speciation.
Any physical nonliving feature that prevents two populations from exchanging genes.
Convergent
One example of this is cacti and euphorbias converging.
If 2 distinct unrelated species occupy the same or similar habitats, natural selection may favor the phenotypes of one species.
Phyletic
Seed Dispersal
Wind, flood, streams, etc. are all good examples of how seeds may be dispersed.
Seeds or fruits that are spiny or gummy are able to stick to the fur or feathers of some animals.
Though fruits and seeds typically fall close to the parent plant, some have long-distance dispersal mechanisms.
Vegetative Propagation
Alleles that arise at various sites ultimately join together through gene flow, then miosis and other systems that create many combinations.
If a species produces small, mobile pieces that reproduce vegetatively, these contribute to gene flow.
Pollen Transfer
Wind-distributed pollen can travel extreme distances.
Animal-mediated pollination
Example: Bees carrying pollen to and from flowers.
Example: Birds carrying small amounts of pollen.
Another form of pollination dependent on the movement of animals for pollination.
Pollen grains each carry one full haploid genome.
Rates of Evolution
It is difficult to identify the presence of particular alleles unless they have an easily identifiable effect.
Evolutionary changes that result in the loss of a structure or metabolism can appear very quickly.
If a feature becomes selectively disadvantageous, many of the mutations that disrupt its development become selectively advantageous.
Due to disruptive mutations occuring more often than not, decay can occur very quickly.
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