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Population Genetics and Evolution (Evolution (Possible due to genetic…
Population Genetics and Evolution
Evolution
Gradual conversion of one species into others
Possible due to genetic mutation
Some mutations are advantageous over others in the environment they inhabit, resulting in change in gene pool, and may eventually result in new species
Other mutations are disadvantageous and may either kill the organism or lead to them being outdone by other, more fit individuals
These are a couple of the fundamentals of Natural Selection
Natural Selection was discovered by Charles Darwin and Alfred Russel Wallace independently
Extremely slow process that takes millions of years to produce obvious changes in organisms
Unless you're about to be the first eukaryotic cell, then that doesn't apply to you
Let it be known that one of the most influential events in history came about because a unicellular organism pressed the mercy button over the fight button
Essential to all biology
Population Genetics
The abundance of different alleles in a population and how this abundance increases, decreases, or stays the same over time
The alleles of all the sex cells in a population is called the population's gene pool
The ratio of different alleles in the gene pool will remain fairly consistent year to year if only sexual reproduction is considered
Factors that cause gene pool to change
Apparently not sexual reproduction
Mutation
Introduction of new alleles, lowering ratio of other alleles
If the mutation makes the organism more fit, we can expect a greater displacement in ratio
Accidents
Think the meteor that wiped out the dinosaurs and cleared the way for mammals, or, on a smaller scale, a volcano erupting and destroying the ecosystem
These are cataclysmic events that practically no organism is safe from
Whether or not an organism survives these events is mostly by chance
Some more minor events can weed out organisms that aren't fit to cope with it, resulting in trees that can withstand forest fires, for instance
The fewer there is of a certain allele, the smaller the events are that are capable of eliminating it
Artificial Selection
Gene pool is purposely altered by humans
Gave us strawberries that don't look like they had a very bad day and dogs in every shape and size
This is done by looking for the most favorable genes in nature and breeding them with one another
Natural Selection
Most significant influence on gene pool
'Survival of The Fittest'
Occurs under two conditions
Population must produce more offspring than their habitat can support
Plants have an easy time with this; they produce hundreds of seeds in their lifetime
One generation must have individuals with differing alleles
An individual isn't more fit for their environment than an identical individual, so their survival would be based purely on chance, not what they can pass on
Refers to differential survival among organisms with differing genotypes
Fitness is decided by several different factors, which aren't all equally important, and their importance is always subject to change
Factors that don't effect natural selection
Purpose
Intention
Planning
Voluntary Decision Making
Book goes to great lengths explaining this idea, but essentially says that organisms only act in the manner that lead to the survival and opportunity for reproduction of those it has descended from
Rates of Evolution
Very
Very
Very
Slow
It takes an organism with a vastly superior phenotype to immediately out-compete the other organisms of its population
Some plant species have persisted for tens of millions of years without diverging into a new species
The faster rates still take around half a million years
These situations usually require putting an existing species in a completely new environment that forces species differentiation
Similar situations
Speciation
A process in which a population becomes a new species distinct from what it was before
A general definition of species is a group of organisms that exclusively produces fertile offspring only with other members of the group
Occurs in two possible ways
Phyletic Speciation
One species changes so much it must be considered a new species
This is able to occur because the beneficial alleles that result in speciation moves evenly throughout the entire species
This physical movement of alleles is called gene flow
Many methods of spreading alleles exist in plants
Pollen Transfer
Each grain of pollen contains a complete haploid set of chromosomes
Travels long distances
Can be transported utilizing animals called pollinators
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Seed Dispersal
Some seeds can travel great distances through wind or water
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Vegetative Propagation
These make it possible for an entire species to be homogeneous, or to have a consistent ratio of alleles throughout the species
Divergent Speciation
Some populations of a species become a new species, while others remain the same
May happen when gene flow fails to maintain homogeny throughout the species
Populations of the same species in different regions that have a differing gene pool are referred to as reproductively isolated
Any physical nonliving feature that contributes to the reproductive isolation of populations is called an abiological reproductive barrier
Speciation under these conditions is called geographic speciation
Any living feature that contributes to the reproductive isolation of populations is called a biological reproductive barrier
One example would be pollinators not recognizing a flower because of a mutation resulting in a different color
This may result in a flower not being able to reproduce with nearby flowers of the same species
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More concerning pollinators here
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Types of biological reproductive barrier
Prezygotic Isolation Mechanism
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Postzygotic Isolation Mechanism
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One type of divergent speciation is called adaptive radiation
This is when a species arrives in a place with plentiful resources and little to no competition
The first individuals are called the founders
All offspring will greatly resemble the founders
The resulting population will have a higher tolerance for different alleles due to this
The developing population will have a very rapidly changing gene pool due to its small size
This phenomenon is called genetic drift
Soon results in heterogeny
Convergent Evolution
Animals with similar niches in similar habitats evolve similarly
Birds and bats, dolphins and sharks, wolves and lions
Evolution and The Origin of Life
Main hypothesis to origin of life is chemosynthesis
Long Explanation
Over millions of years, pre-existing chemicals react with one another until all the molecules required for life are created. This eventually results into protocells, which then are subject to natural selection, which leads to the eventual speciation of all living organisms
Four conditions must be met for chemosynthetic origin
Right Chemicals
Appropriate Energy Sources
More than 6,000 years of time
An absence of molecular oxygen
Works out, since oxygen created by plants obviously comes about after origin of life
Short Explanation
Chemicals made literally everything. We're just talking about how it made life itself this time
Chemicals present in the atmosphere before the origin of life
When the Earth was still mostly rocks and volcanoes, its atmosphere was composed of mostly hydrogen
Because hydrogen's a lightweight, it was mostly pushed out into space.
Earth, using the power or rocks, created a second atmosphere from rock gases released by the aforementioned rocks as well as cool space rocks
Could be debated that every rock is a space rock since Earth itself is a space rock
This second atmosphere was also a reducing atmosphere, because it has reducing agents
Today's atmosphere derived from this second atmosphere along with oxygen produced by...
Photosynthesis
