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Population Genetics and Evolution (Speciation (Phyletic speciation (pollen…
Population Genetics and Evolution
Population Genetics
deals with the abundance of different alleys w/in a population
how the abundance of an allele increases, decreases or remains the same with time
total number of alleles in all the sex cells of all individuals of a population makes the gene pool
factors that cause the gene pool to change
all genomes are subjected to mutagenic facts and mutations offer continually
existing alleles decrease, new alleles increase
significance of mutation depends on population size
accidents are events to which an organism cannot adapt
ex. a large meteorite colliding with Earth
all organisms and alleles would be destroyed
if the allele just formed a new mutation, that mutation would be permanently destroyed
Artificial selection: process where humans purposefully change the allele frequency of a gene pool
common use from breeders and farmers
use it to enhance the plant in one form or another
Natural selection: the most significant factor causing gene pool changes "survival of the fittest"
in order for process to happen two conditions must be met first
population must produce more offspring than can possibly grow and survive to maturity
secondary condition: progeny must differ from each other in their types of alleles
factors that are not part of natural selection:
purpose, intention, planning or voluntary decision making
Situations where Natural Selection don't operate
a good wy to understand natural selection is to know when it doesn't work
can't work when all individuals of a population are identical
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a good example is freshly planted crops of the same seed
Speciation
natural selection has caused a new species to evolve, which is called speciation
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Phyletic speciation
one species gradually becomes so changed that is must be considered new
generally takes millions of years for a new species to evolve into a new one
critical feature* beneficial allele arise and are selected fir, become spread throughout entire population. Called gene flow
animal and insects also contribute to gene flow
pollen transfer carry one full haploid genome, and all alleles of a plant are present in pollen grains
new allele is carried by some pollen grains allowing it to travel a great distance
if pollen grains sperm cells fertilize an egg, a new seed develops with an embryo which has all new DNA
*seed dispersal, most fall close to parent but some have creative ways to move long distance
can be carried by wind, floods and stream flow
sticking to the fur of different animals, trapped above water on different debris
*vegetative propagation, species produces small, mobile pieces that reproduce vegetatively also contribute to gene flow
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Divergent speciation
if gene flow doesn't keep the species homogeneous through out entire range divergent speciation occurs
abiological reproductive barriers: any physical, nonliving feature that prevents two populations from exchanging genes
original species can divide into two or more populations and can't interbreed
commonly referred to as allopatric
mountain ranges are a good example because pollinators do not fly across entire mountain
*biological reproductive barrier; any biological phenomenon that prevents successful gene flow
flower color, shape or fragrance can be features that cause this
mutations that cause color change
when two species are isolated and reproduce together it can cause sympatric speciation
*adaptive radiation; special case of divergent speciation
species rapidly diverges into many new species over an extremely short time line
Convergent Evolution
if two species share the came habitats, natural selection may only favor certain phenotypes
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two species evolve and resemble each other strongly
Evolution and the Origin of LIfe
Conditions of Earth Before the Origin of Life
the earth has many gases on around the planet
we have a second atmosphere because the first one was lost to space
this second atmosphere was a reducing atmosphere due to the lack of molecular oxygen
*energy sources
UV and gamma radiation was used long ago for energy,
came from the sun and ws locked in the second atmosphere letting of quanta and atoms
heat is another energy used to power reactions
electricity is the biggest though, the lighting triggered chemical reactions which makes it possible for rain to reach the surface