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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Population Genetics
situations in which natural selection does not operate
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if all individuals of a population are identical genetically
if its is impossible to become adapted to a certain condition
multiple selection pressures
drought
cold
insect attack
need for pollunators
pathogenic fungus
efficiency of their own metabolism
need for mechanism to disperse their seeds
Factors that cause the gene pool to change
artificial selection
the process in which humans purposefully change the allele frequency of a gene pool
example: selective breeding of crop plants and domestic animals
natural selection
usually described: survival of the fittest
most significant factor causing gene pool changes
those individuals that are most adapted to an environment survive, whereas those less adapted do not.
accidents
events to which an organism cannot adapt
example: collision of large meteorite with Earth
factors that are not part of natural selection
intention
planning
purpose
voluntary decision making
Mutation
mutations occur continually
because of mutation, existing alleles decrease in frequency and new alleles increase
all geneomes are subjected to mutagenic factors
Rates of Evolution
very few mutations produce a new phenotype so superior that it immediately out competes all other members of the population
at the extremes there are many species of of seedless plants that have persisted for tens of millions of years without diverging into new species
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most populations are relatively well adapted to their habitat or they would not exist
Speciation
divergent speciation
biological reproductive barriers
adaptive radiation
abiological reproductive barriers
convergent evolution
phyletic speciation
seed dispersal
the fruits and seeds of some plants fall close to the parent
many species are carried long distance in various ways
floods
stream flow
rafting
spiny or sticky fruits and seeds can stick to the fur or feathers of animals
winds
vegetative propagation
if a species produces small mobile pieces that reproduce vegatatively these too contribute to gene flow
pollen transfer
pollen grains each carry one full haploid genome
all alleles of a plant are present in its pollen grains
Evolution and the Origin of Life
aggregation and organization
early metabolism
formation of polymers
chemicals produced chemosynthetically
oxygen
conditions on earth before the origin of life
the presence of life
