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Population Genetics and Evolution (Speciation (Can occur in two…
Population Genetics and Evolution
Population Genetics
Deals with the abundance of different alleles within a population
Also deals with the manner in which the alleles increase, decrease, or remain the same over time
Genetic recombination that occurs during sexual reproduction is only important if the two partners have different genotypes
Crossing-over
Increases genetic diversity in populations
Gene pool
Total number of alleles in all the sex cells of all individuals of a population
Factors that cause the gene pool to change
Mutations
All genomes are subjected to mutagenic factors
Whether or not a mutation is significant depends in part of the population's size
Accidents
Events to which an organism cannot adapt
Such as a meteorite striking Earth
If an individual with a special allele was the only one with that specific allele in the blast zone, it would no longer exist
Volcanic eruption
Infrequent floods
Hailstorms
Drought
Artificial selection
Process in which humans purposefully change the allele frequency of a gene pool
An example would be selective breeding of crop plants and animals
Natural Selection
Is the most significant factor causing gene pool changes
The most adaptive survive
Factors that are not part of Natural selection
Purpose
Intention
Planning
Voluntary decision making
Rates of Evolution
Most populations are relatively well adapted to their habitat, or they wouldn't exist
Very few mutations produce a new phenotype that outcompetes all of the other members in a population
Seedless plant such as lycopods have persisted for millions of years without diverging into a new species
It's difficult to identify the presence of certain alleles in a population unless the phenotype is easily identifiable
Speciation
As natural selection works on a population for many generations the phenotype changes and has caused the species to evolve
Two organisms are considered to be members of distinct species if they can't produce fertile offspring
An exception would be between the maples in the western U.S and those of the eastern U.S
Their pollen can not travel that far
Can occur in two fundamental ways
phyletic speciation
In which one species gradually becomes so changed that it must be considered a new species
Gene flow
Occurs in many ways
Pollen transfer
Pollen grains each carry one full haploid genome
All alleles of a plant are present in its pollen grains
seed dispersal
Several ways seeds can be dispersed
Winds
floods
stream flow
Also be carried o islands by rafting
Which they are trapped above water on tangled mat or floating debris
vegetative propagation
A species that produces small mobile pieces that reproduce vegetatively
Help contribute to gene flow
divergent speciation
In which some populations of a species evolve into a new, second species while other populations either continue unchanged, or evolve into a new third species
Divergent speciation
If gene flow does not keep the species homogeneous throughout its entire range
Reproductively isolated
Two fundamental causes
abiological
Original species is physically divided into two or more populations that cannot interbreed
If speciation results it is known as allopatric or geographic speciation
biological reproductive barriers
Any biological phenomenon that prevents successful gene flow
known as biological reproductive barrier
Sympatric speciation
When two groups become reproductively isolated even though they grow together
Evolution and the Origin of Life
The most seriously considered hypothesis about the origin of life on Earth is that of chemosynthesis
It attempts to model the origin of life using only known chemicals and physical processes
Conditions on Earth before the origin of life
Earth condensed from gases and dust about 4.6 billion years ago
Was initially hot and rocky and had an atmosphere composed of mostly hydrogen
Since hydrogen is a light gas most of this first atmosphere was lost into space
The second atmosphere replaced it, and was made of gases released from he rock matrix composing Earth and from meteorites
The early second atmosphere was a reducing atmosphere due to the lack of molecular oxygen and the presence of powerful reducing agents
Energy sources
Intense UV
Gamma radiation from the sun
heat
second heat source was radioactive decay
Electricity from lightning
Time available for the origin of life
Basically had no limits
Because of the lack of free molecular oxygen
The presence of life
The chemistry of living creatures is more complex than that of nonliving objects
But it does not possess any unique properties
It is important for us to understand the process in their complexity
