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Population Genetics and Evolution (Evolution and the Origin of Life…
Population Genetics and Evolution
Population Genetics
different alleles within a population and how it increases decreases with time
sexual reproduction
cross of parents with different genotypes
yields genetic diversity
gene pool
total number of alleles in sex cells of all individuals of a population
Hardy & Weinberg
sexual reproduction= constant ratio of 60%:20%:15%:5%
sexual reproduction does not change gene pool of population, unless other factors take place
Factors that cause change of the gene pool
Mutation
all genomes subjected to mutagenic factors
significance of mutation depends on the size of the population
accidents
events an organism can not adapt
kills all presence of those alleles
accidents act as a selective force
weak alleles lost
strong survive to be passed on
meteorite
volcanic eruption
droughts or floods
small or large events
artificial selection
humans change allele frequency of a gene pool on purpose
selective breeding
crops
flower color
resistance to disease
survive with less water
flowering longer
animals
often carried out with in conjunction of artificial mutation
acridine dyes
UV light or gamma rays
Natural Selection
survival of the fittest
individuals more adapted to a situation or environment live and less adapted do not
evolution
differential survival
survival of organisms with different phenotypes
two conditions must be met before natural selection can occur
population must produce more offspring than can possibly grow and survive to maturity in the habitat
Progeny must differ from each other in their types of alleles
Factors not part of natural selection
purpose
intent
planning
voluntary decision making
voluntary actions are the only way these can apply
humans and other primates
Situations in which natural selection does not operate
all individuals of a population are exactly identical genetically
environment with no competition occurring
Multiple selection pressures
loss of individuals and reproduction due to more then one factor
loss of a mutation that could be beneficial to survival due to death of host or no reproduction
accident
insect attack
drought
cold
pathogenic fungus
Rates of Evolution
most populations are well adapted to their current environment
very few mutations produce new phenotypes that is superior
most studies concern changes in gross structures
flowers
leaves
fruits
shoots
trichomes
most structure or metabolism changes come quickly
many mutations become selectively advantageous
Speciation
natural selection causing a new species
results from so much change in phenotypes of the species
considered a new species when fertile offspring aren't produced from two organisms
some exceptions exist
hybrids
occurs two ways
phyletic speciation
so changed= new species
divergent speciation
some of population evolves into a new species
rest remain the same
Phyletic Speciation
new beneficial alleles spread through out entire population
gene flow
pollen transfer
grains carry one full haploid genome and all alleles
pollen can move to very distant pants
results in fertilization of a different type of plant
contains new alleles
seed dispersal
parents have long dispersal mechanisms
carried to new place where it can transfer alleles
vegetative propagation
small, mobile pieces that reproduce vegetatively
Divergent Speciation
if alleles do not reach individuals in one part, then two regions are reproductively isolated
abiological reproductive barrier
physical, nonliving feature that prevents exchanging of genes
biological reproductive barrier
biological phenomenon preventing successful gene flow
Adaptive Radiation
divergent evolution in which species diverge into many new species over a short time
entering new habitat with no competition or environmental stress
genetic offspring resemble the founder
Convergent evolution
unrelated species occupy the same habitat, natural selection favors same phenotype
two evolve to resemble one another
two cannot converge to the point of producing the same species
only phenotypes converge, not genotypes
Evolution and the Origin of Life
species of today evolved from those that existed from the past
origin of life
chemosynthesis
chemical and physical processes with no divine intervention
chemicals from earth reacting over millions of years to produce the molecules of today necessary for life
four conditions required
right inorganic chemicals
appropriate energy sources
time
absences of destructive O2
Oparin and Haldane 1942
conditions on earth before the origin of life
chemicals present in atmosphere
1st atmosphere lost due to hydrogen being a light gas
2nd atmosphere produced from release of rock matrix composing earth
H2S
NH3
CH4
water
early reducing atmosphere
energy sources
UV and gamma radiation
heat
electricity
volcanoes producing lightning
time available for origin of life
had no limits due to lack of free molecular oxygen
chemicals produced chemosynthetically
S. Miller invents experiment using varying atmospheric conditions to produce organic compounds
all small molecules essential to life produced this way
amino acids
lipids
sugars
nitrogen bases
formation of polymers
monomer had to polymerize to give rise to life
requires high concentration of monomers
aggregation and organization
aggregation of chemicals components into masses with organization
early metabolism
metabolic pathways begin to form
natural selection favoring extension
oxygen
evolution of chlorophyll
a
and photosynthesis that liberates oxygen = two consequences
world rusts
aerobic respiration
presence of life
can not really for sure at which stage life came into being
