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Population genetics and evolution (Evolution and the origin of life…
Population genetics and evolution
Population genetics
Situation in which natural selection does not operate
If survival is universal, natural selection does not occur
This occur in newly opened habitats such as plowed fieds
Genetically identical individuals
Multiple selection pressures
because of drought, cold, need for pollinators and need for a mechanism to disperse their seeds.
with mutation the presence of fungi not only anti-fungal allele but for the cold hardiness allele, just by coincidence
Cause loss of individual and reduced in reproduction
Factors that cause the gene pool to change
Accidents
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Example-: volcanic eruption produce gases and molten rocks that destroy everything, infrequent floods, hailstorms or drought
Unusual high number of alleles are affected than other alleles
Events to which an organism cannot adapt
Artificial selection
Beneficial plants are collected and used for breeding
Used to produce ornamental plants, alter color of flower and to make the plants hardy
Human purposefully change the allele frequency
Mutation
Mutation depends on population size
The changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations
All genomes are subjected to mutagenic factors, and mutations occur continually
Natural selection
The progeny must differ from each other in their type of allele
Population must produce more offspring that can possibly grow and survive
Genetic diversity helps in differential survival
Other factors
Purpose, intention, planning or voluntary decision
The resistance of plants to different things is their preferential survival
Those factors that are not a part of natural selection
Speciation
Divergent speciation
Abiological reproductive barriers
Allopatric; Geographic speciation
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Physical, non living features that prevent from exchanging genes
Biological reproductive barriers
Biological phenomenon that stops gene flow
Leads to the extinction of one species
Sympatric speciation
Adaptative radiation
Special case of divergent evolution
Species rapidly diverse into many new species over short time
can also occur in mainland population if the environment changes suddenly and eliminates the dominant species
Convergent evolution
Two may evolve to the point that they resemble each other strongly
example-: Cacti and euporbias
If two distinct, unrelated specie occupy the same or similar habitats
Formation of desert is also favored a similar phenotype
Phyletic speciation
seed dispersal
Wind, flood, streams carries seed to different places
Some seed dispersal are close and some are long distance
Transferred seed germinate, grows and reproduced to new plant
Vegetative propagation
Small, mobile pieces that reproduce vegetatively will also contribute gene flow
Alleles that arise at different geographic part come together by gene flow
Pollen transfer
All alleles of a plant are present in pollen grains
Animal-mediated pollination also contribute to gene flow
Carries one full haploid genome
Rates of evolution
Very few mutation produce a new dominant phenotype
Species of seedless plants have persisted millions of years
Allelic composition of a population could change rapidly within few generation
Rapid speciation is occurring in groups of asters in Hawaii
evolution involve mutation, all the mutations are not advantageous
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Evolution and the origin of life
Aggregation and organization
Second step of chemical evolution
Aggregates are controlled by relative solubility
Aggregates are not alive so they cannot store genetic information
Early metabolism
Metabolic pathway two step long involving enzyme started
Glycolysis must have evolved early because it is present in virtually all organisms
Heterotroph aggregates absorb all materials from the ocean and modify only few
Formation of polymers
Formation of seaside pools at high tide
Monomers present in earth has to polymerize if life were to arise
Absorption by clay particles
Chemicals produced chemosynthetically
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Direct analysis of meteorites and lunar samples reveals what has actually happened in non living environment
Rock sample from moon got various organic compounds
Oxygen
That allows world to rust, evolution of aerobic respiration
Todays atmosphere derived from early second atmosphere adding oxygen
Evolution of chlorophyll a and photosynthesis
Condition on earth before the origin of life
Energy source
Coalescence of gas, radioactive decay
Foremost energy was UV and gamma rays
Time available for the origin of life
Chemosynthetic origin of life had no limits
Without oxygen no agents was present to cause the breakdown and decomposition
Chemical present in the atmosphere
Seriously considered hypothesis is chemosynthesis
Initially earth was hot and rocky with abundant hydrogen and was replaced by second atmosphere
Early second atmosphere was reducing due to lack of molecular oxygen
The presence of life
We can find fossil of early prokaryote that lived approximately 3.5 billion years ago
The complexity in organisms increases with the evolution
Transition from completely inorganic compounds to living bacteria
