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Chapter 18: Population Genetics and Evolution - Coggle Diagram
Chapter 18: Population Genetics and Evolution
Chapter Outline
Population Genetics
What causes gene pool changes?
Where natural selection doesn't work
Multiple selection pressures
Rates of Evolution/Speciation
Speciation
Divergent
Phyletic
Convergent evolution
Evolution and Origin of Life
Conditions before life
Chemosynthetic chemicals
Polymerization
Organization/Aggregation
Early Metabolism
Oxygen
The presence of life
Concepts
Evolution
The gradual conversion of one species into a or several new species
occurs through natural selection
Mutations
Cause new alleles/genes to arise that affect an individual's fitness
Deleterious: Individual will not thrive
Beneficial: Individual thrives
As it continues, the abundance of alleles cause a change in phenotype
Extremely slow process that may take millions of years
Scientific Revolution
Discovery of natural selection
Alfred Russel Wallace
Charles Darwin
Origin of Species
1859
Concept revolutionized adaptation theory
Population Genetics
The abundance of alleles within a population
Increases
Decreases
remains constant
Genetic Recombination
occurs during sexual reproduction
is only important if two partners have different genotypes
crossing over increases genetic diversity
Gene Pool
The total number of alleles in the sex cells of all individuals of a population
Hardy and Weinberg
demonstrated mathematically that the gene pool ratio remains constant
Factors that change the gene Pool
Mutation
All genomes are subjected to mutagenic factors
existing alleles decrease in frequency while new alleles increase
significance depends on population size
Accidents
events to which an organism cannot adapt
when all organisms and their alleles are eliminated
volcanic eruptions, infrequent flooding, hailstorms, droughts
Continental drift of Antarctica was an accident
Artificial Selection
The process in which humans purposefully change the allele frequency
Plants with beneficial qualities are bred to produce populations with those alleles
often carried out in conjunction with artificial mutation
acridine dyes
irradiation
Natural Selection
survival of the fittest
individuals most adapted to an environment survive
two conditions must be met
population must produce fertile offspring
progeny must differ from each other in terms of alleles
does not cause mutations
Does not occur at the individual level
Where Natural Selection Does not Operate
If all individuals of a population are identical genetically or adaptation is impossible
If survival is universal
occurs in newly opened habitats
Multiple Selection Pressures
Loss of individuals and reduced reproduction not caused by a single factor
attack
drought
cold
ability to reproduce
metabolic efficiency
An allele that improves fitness is potentially advantageous but not guaranteed to improve fitness
Loss of this allele would be an accident
Plieotrophy
Side effects, often disadvantageous
Rates of Evolution
Most populations relatively well adapted
very few mutations produce a superior phenotype
Difficult to identify particular alleles unless the phenotypic effect is easily identifiable
Evolutionary studies of plants concern
flowers
leaves
fruits
shoots
trichomes
As systems become more intricate, the probability of a beneficial random change decreases
Because disruptive mutations outnumber beneficial ones, loss can occur rapidly
Convergent Evolution
If a phenotype is deemed favorable, two distinct unrelated species may evolve to be very similar
Speciation
The change in frequency of various alleles and phenotype to the development of a new, genetically distinct species
A new species exist when they do not produce fertile offspring
If two plants freely interbreed in nature-same species, if no interbreeding occurs they are separate species
Occurs in two fundamental ways
Phyletic Speciation
one species gradually becomes so changed it is considered a new species
Millions of years often required for a species to evolve into a new one
gene flow
The movement of alleles physically through space
occurs by pollen transfer, seed dispersal, and vegetative propagation
Pollen Transfer
Pollen grains each carry one full haploid genome
if a new allele is carried by pollen, it can move to very distant plants
Animal-mediated pollination contributes to gene flow
Seed duspersal
many species have long-distance dispersal mechanisms
seeds
carried by wind, floods, stream
rafting
stick to fur or feathers of animals
Vegetative Propagation
produces small, mobile pieces to reproduce
alleles that arise at various geographic sites ultimately come together by gene flow, then are rearranged
Divergent speciation
some populations evolve into a second species while other continue unchanged or develop a third species
Reproductive Isolation
When alleles that arise in one part of the range do not reach individuals in another part
occurs in two fundamental ways
Abiological Reproductive Barriers
Any physical, nonliving feature that prevents two populations from exchanging genes
Original species is physically divided into two or more populations that cannot interbreed
if speciation results it is called allopatric or geographic speciation
Biological Reproductive Barriers
Any biological phenomenon that prevents successful gene flow
When two groups become reproductively isolated even though they grow together is sympatric speciation
evolutionary changes in pollinators
Prevention of pollination and fertilization is caused by prezygotic isolation mechanisms
postzygotic internal isolation barriers
when each organism is phenotypically unique to where they can no longer interbreed
Hybrid Sterility
two populations produce viable seed that grows into a sterile plant
unable to complete meiosis
hybrid inviability
After internal isolation barriers are established
divergence becomes rapid
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Adaptive Radiation
A species rapidly diverges into many new species over just a few million years
usually occurs when there is little to no competition
colonization of newly formed islands
initially devoid of all life
eventually a seed arrives, free from competition
successful colonization
All offspring greatly resemble founder individuals because founder gene pool contains only two sets of alleles
more subject to accidents
gene pool can change rapidly and cause genetic drift
based largely on physical environmental factors
Evolution and the Origin of Life
The species present today have evolved from those which existed in the past, which evolved from those that existed before them
Chemosynthesis Hypothesis
Attempts to model the origin of life using only known chemical and physical processes
Rejects divine intervention
postulated that chemical reactions produced aggregations over millions of years
For this to occur, Primitive Earth must have had
The right inorganic chemicals
Appropriate energy sources
time
absence of destructive O2
a plausible model
Conditions on Earth Before Life
Chemicals Present in the Atmosphere
Hydrogen
most of the first atmosphere lost into space
Earth condensed from gases and dust about 4.6 billion years ago
Second atmosphere
reducing atmosphere
created by release of gases from Earth's rock matrix and meteorite bombardment
H2S, NH3, CH4, and H2o
Molecular o2 absent
Energy Sources
Second atmosphere was exposed to powerful energy sources
UV Radiation
Gamma radiation
Heat
the coalescence of gas and dust
Electricity
Time Available
No limits due to lack of oxygen
no agent present to cause molecular decomposition
1.1 billion years may have elapsed between solidification of earth and formation of life
Ocean = Primordial Soup
Contained water, salts, and organic compounds
Chemicals Produced Chemosynthetically
S. Miller
Performed the first experimental chemosynthetic hypothesis test in 1953
constructed a container with boiling water in the bottom and an electrified reducing atmosphere in the top
Electrodes discharged sparks, steam rose from the boiling, mixed with the atmosphere, and fell back into water to be recycled
Let the experiment cycle for a week
found many different substances in the solution including amino acids
The interior of meteorites have contained sugars, alcohols, amino acids, and nitrogenous bases
Formation of Polymers
required high concentrations of monomers
monomers accumulated in the sea and polymerized
Could have been assisted by absorption by clay particles
Clay particles similar to enzymes
Clay contains ions of iron, magnesium, calcium, phosphate, and other charged groups
Aggregation and Organization
Hydrophobic material formed lipid bilayers
First aggregates would have formed at random controlled by relative solubility
Aggregates not considered to be alive, they are without genetic information
Without genetics, natural selection cannot occur
Existence of aggregates may have had a significant effect on the chemistry of the oceans
assisted in the formation and destruction of more complex molecules and polymers
RNA may have been first heritable molecule
Early Metabolism
Early Aggregates would have been complete heterotrophs
Aggregates that are capable of synthesizing scarce molecules have a strong selective advantage to grow and reproduce
Natural selection would favor those with more efficient metabolisms
No preformed organic molecules necessary
Glycolysis evolved
aggregates begin to absorb ATP
First ion pumps powered by light
Oxidative transport still nonexistent because of the lack of free molecular oxygen
Oxygen
Consequenses
allowed world to rust
created conditions that selected for aerobic resperiation
Before, photosynthesis involved bacteriochlorophyll
Oxidative photosynthesis occurred 2.8 billion years ago
Proven by the period of rusting apparent in sedimentary rocks
without iron to stabilize the oxygen, the oxygen levels of earth may have become toxic
The Presence of Life
The chemosynthetic theory delineates no absolute demarcation between living and nonliving objects
The physics of living and nonliving systems is identical
More important to understand life's processes in their complexity