Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Rates of Evolution
Evolution usually occurs over a long period of time, however, some species have changed rapidly.
Divergent speciation in which some populations of a species evolve into a new, second species while other populations either continue relatively unchanged as the original, parental species or evolve into a new, third species.
If alleles that arise in the one part of the range do not reach individuals in another part, the two regions are reproductively isolated.
Reproductive isolation can occur in many ways, but the two fundamental causes are abiological and biological reproductive barriers.
Abiological Reproductive Barriers
nonliving feature that prevents two populations from exchanging genes
Allopatric is when a species divided into two or more populations cannot interbreed
Also known as geographic speciation
Biological Reproductive Barriers
Any biological phenomenon that prevents successful gene flow
When two groups become reproductively isolated even though they grow together, the result is sympatric speciation
When two species occupy the same habitats and develop the same phenotype
Phyletic speciation in which one species gradually becomes so changed that it must be considered a new species.
This movement of alleles physically through space is called gene flow.
Occurs in many ways such as:
Seeds can be carried by wind, floods, and stream flow.
If a new allele is carried by some of the pollen grains, it can move to very distant plants.
If a species produces small, mobile pieces that reproduce vegetative, these too contribute to gene flow.
Natural Selection has caused a new species to evolve, a process called speciation.
Evolution and the Origin of Life
Aggregation and Organization
The next step in the possible chemical evolution of life would have been aggregation of chemical components into masses that had some organizations and metabolism.
Conditions on Earth Before the Origin of Life
Chemicals Present in the Atmosphere
Hydrogen was the first atmosphere, but it was such a light gas that it was lost in space.
A second atmosphere was produced by release of gases from the rock matrix composing Earth and from heavy bombardment by meteorites
Time available for the origin of life
Basically no limit
The aggregates would have been complete heterotrophs, absorbing all material from the ocean and modifying only a few molecules.
The Presence of Life
The chemosynthetic theory postulates a long series of slow, gradual transitions from completely inorganic compounds to living bacteria.
Formation of Polymers
Monomers present in the early ocean had to polymerize if life were to arise, but polymerization required high concentrations of monomers.
The atmosphere present today was derived from the early second atmosphere by this addition of oxygen from photosynthesis.
It is an oxidizing atmosphere
Chemicals Produced Chemosynthetically
Meteorites interiors, uncontaminated by soil and the fall through the atmosphere have:
Nitrogenous bases that occur in nucleic acids
Multiple Selection Pressures
In many cases, the loss of individuals and reduced reproduction are not caused by a single factor.
Factors that Cause the Gene Pool to Change
All genomes are subjected to mutagenic factors, and mutations occur continually.
Accidents are events to which an organism cannot adapt, such as the collision of a large meteorite with Earth.
Artificial Selection is the process in which humans purposefully change the allele frequency of a gene pool.
Natural Selection, which is the most significant factor causing gene pool changes, is usually described as survival of the fittest.
Factors that Are Not Part of Natural Selection
Voluntary Decision Making
Situations in which Natural Selection Does Not Operate
It cannot operate if all individuals of a population are identical genetically or if it is impossible to become adapted to a certain condition.
If survival is universal
Newly opened habitats
Sides of a road cut
Recently burned area
Recently flooded plain covered with rich sediments
Population Genetics deals with the abundance of different alleles within a population and the manner in which the abundance of a particular allele increases, decreases, or remains the same with time.
The total number of alleles in all the sex cells of all individuals of a populations is the gene pool