Download Mechanisms of Evolution Notes

MECHANISMS OF EVOLUTION
How do organisms adapt to their environment?
GENETIC DRIFT
SOME INDIVIDUALS MAY BY CHANCE, AND NOT
BEC AUSE OF “FITNESS,” LEAVE MORE DESCENDANTS
AND THEREFORE PASS ON THEIR GENES
FOUNDER EFFECT
• a new colony is formed by a few
members of the original population
BOTTLENECK
• having an event that kills off
members of a species randomly by
chance.
GENE FLOW
THE RANDOM MOVEMENT OF INDIVIDUALS INTO AND
OUT OF POPULATIONS, MIGRATION, INCREASES GENETIC
VARIATION WITHIN A POPULATION
• Gene Pool – All the alleles in a populations genes. In other words every
form of a trait
• Allelic Frequency – the % of any specific allele w/in a gene pool
• Genetic Equilibrium – allele frequency remains the same over generations
• Populations in genetic equilibrium are not evolving
MUTATION
CHANGE IN A GENE; ALTERATION OF A
NUCLEOTIDE SEQUENCE
• Negative more than likely causes death
• Positive may be beneficial and passed on
to future generations
EX: A mutation causes two green
beetle parents to have a brown
beetle
NATURAL SELECTION
• Stabilizing Selection (birth weight)
• Direction Selection (peppered moth)
• Disruptive Selection (limpet shell color)
STABILIZING SELECTION
NATURAL SELECTION THAT FAVORS AVERAGE
INDIVIDUALS
DIRECTIONAL SELECTION
NATURAL SELECTION THAT FAVORS AN EXTREME
FORM OF A TRAIT
DISRUPTIVE SELECTION
INDIVIDUALS W/ EITHER EXTREME FORM OF
A TRAIT
Shifts from the Average Cause Speciation:
Directional Selection
Stabilizing Selection
Disruptive Selection
SPECIATION
• Species – organisms that look alike can interbreed to produce fertile offspring
• Speciation – evolution of a new species.
• Organisms within the same species have reproductive success ( ability to pass
genes onto the next generation in a way that they too can pass on those genes.)
Reproductive
Success
SPECIATION
• Allopatric Speciation (Geographic Isolation)
SPECIATION
• Sympatric Speciation (reproductive isolation): develop different mating
seasons, mating rituals, and reproductive structures.
These Meadowlarks have different
songs that separate them behaviorally.
These Bowerbirds live in the same area but have
different mating seasons and rituals.
PATTERNS OF EVOLUTION
• Coevolution: two species evolve in close relationship with each
other.
• Ex: mutualistic relationships
PATTERNS OF EVOLUTION
• Convergent Evolution: organisms not closely
relate, independently evolve similar traits (to
adapt to similar environments.)
PATTERNS OF EVOLUTION
• Divergent Evolution: one
species turns into many
new species in a
relatively short time
• Ex: Adaptive Radiation:
ancestral species
evolves into an array of
species to fit a particular
environment or niche
RATE OF SPECIATION
• Gradualism: – idea that species
originate through a gradual change
of adaptations
• Punctuated Equilibrium : things
staying the same for a period of
time then rapidly changing due to
a catastrophic event