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Population Genetics and Evolution (Evolution and the Origin of Life (The…
Population Genetics and Evolution
Population Genetics
Factors that Cause the Gene Pool to Change
Mutation
existing alleles decrease in frequency & new alleles increase
Accidents
events to which an organism cannot adapt
Artificial Selection
humans purposefully change the allele frequency of a gene pool
Natural Selection
most significant factor
survival of the fittest
Situations in which Natural Selection Does Not Operate
cannot operate if all individuals of a population are identical genetically
or if it is impossible to become adapted to a certain condition
Multiple Selection Pressures
the plants are also affected by insect attack, drought, cold, need for pollinators
& need for a mechanism to disperse their seeds, as well as the efficiency of their own metabolism
such as the ability of their membranes to pump ions,
the capacity to reduce nitrogen or the efficiency of producing just enough P-protein in the phloem w/o a nonuseful excess
deals w/ the abundance of different alleles within a population
& the manner in which the abundance of a particular allele increases, decreases, or remains the same w/ time
gene pool
total # of alleles in all the sex cells of all individuals of a population
Rates of Evolution
Most populations are relatively well adapted to their habitat, or they would not exist
few mutations produce a new phenotype superior that it outcompetes all other members of the population
It is difficult to identify the presence of particular alleles in a population
unless they result in an easily identifiable effect on the phenotype
As systems become more intricate
the probability decreases that any random change is beneficial
Speciation
Phyletic Speciation
one species gradually becomes so changed that it must be considered new species
Pollen Transfer
Pollen grains each carry 1 full haploid genome
all alleles of a plant are present in its pollen grains
Seed Dispersal
fruits & seeds of some plants fall close to the parent
many species have long distance dispersal mechanisms
can be carried by wind, floods, stream flow
Vegetative Propagation
If a species produces small, mobile pieces that reproduce vegetatively,
these too contribute to gene flow.
Divergent Speciation
some populations of a species evolve into a new, second species
other populations either continue relatively unchanged as the original, parental species
or evolve into a new, third species
reproductively isolated
if alleles that arise in one part of the range do not reach individuals in another part
Abiological Reproductive Barriers
physical, nonliving feature that prevents 2 populations from exchanging genes
Biological Reproductive Barriers
biological phenomenon that prevents successful gene flow
Adaptive Radiation
occurs when species enters a new habitat where little/no competition or environmental stress exists
species rapidly diverges into many new species over an extremely short time
Convergent Evolution
If two distinct, unrelated species occupy the same or similar habitats
natural selection may favor the same phenotypes in each
the two may evolve to the point that they resemble each other strongly
Natural selection has caused a new species to evolve
Evolution and the Origin of Life
Conditions on Earth Before the Origin of Life
chemosynthetic hypothesis
attempts to model the origin of life using only known chemical & physical processes
Chemicals Present in the Atmosphere
Earth condensed from gases & dust about 4.6 billion years ago
atmosphere made of hydrogen
1st atmosphere was lost into space
it was replaces by a 2nd atmosphere
produced by release of gases from the rock matrix
early 2nd atmosphere
reducing atmosphere
Energy Sources
lightining
volcanoes
heat
radioactive decay of heavy elements
uranium & radium
coalescence of gas and dust to form Earth
UV & gamma radiation from the sun
Chemicals Produced Chemosynthetically
1st tests were in 1953 by a graduate student, S. Miller, at the University of Chicago
direct analysis of meteorites & lunar samples reveals what actually happened in nonliving environments
Formation of Polymers
Monomers present in the early ocean had to polymerize if life were to arise
but polymerization required high concentrations of monomers
Absorption by clay particles could have concentrated monomers
clay particles are tiny fragments of rock, they have a regular, crystalline surface
organic molecules adhere to them in a particular orientation
Aggregation and Organization
These first aggregates would have formed basically at random, controlled only by relative solubility
Countless numbers of these aggregates might have formed
and disassociated throughout all of the oceans over millions of years
Early Metabolism
As aggregates continued to consume certain nutrients
any aggregate that could produce an enzyme capable of synthesizing the scarce molecule from an abundant one
would have had a strong selective advantage
there would have been a metabolic pathway 2 steps long involving 2 enzymes
Oxygen
The evolution of chlorophyll a & photosynthesis that liberates oxygen had 2 consequences:
it allowed the world to rust
created conditions that selected for the evolution of aerobic respiration
after chlorophyll a evolved, the raw material for photosynthesis became water
& free molecular oxygen, O2, was released as a waste product
The Presence of Life
The chemosynthetic theory postulates a long series of slow, gradual transitions
from completely inorganic compounds to living bacteria
The chemistry of living creatures is more complex than that of nonliving objects
but it does not possess any unique properties
The physics of living and nonliving systems is identical
it is more important for us to understand the processes in their complexity
