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Transcript
Population Genetics
How populations change over
time
Hardy-Weinberg
• States that without
outside factors acting
on a population, allele
frequencies would
remain the same =
NO EVOLUTION
• Factors affecting
evolution:
–
–
–
–
–
Genetic drift
Gene flow
Nonrandom mating
Mutations
Natural selection
Genetic Drift
• ANY change in allele
frequencies
– Founder Effect:
• occurs when a small
sample of the
population is separated
from the rest
– Bottleneck Effect:
• Population declines to a
very low number and
then rebounds
• BOTH RESULT IN
• Organisms breed with
one another
• Might see
new/uncommon traits
emerge
Gene Flow
• Individuals are always
moving into and out of
habitats based on
competition and/ or
predation
• Immigration and
emigration
• Causes NEW allele
frequencies
Gene Flow
• Introduced species
Purple loosestrife,
originally brought to
North America
accidentally on cargo
ships, reproduces
very quickly and
aggressively, often
crowding out species
like the cattail.
Nonrandom Mating
• Organisms mate with
individuals in close
proximity  promotes
inbreeding
• Could lead to a
change in allele
frequencies
(mutations)
Nonrandom Mating
• ALSO includes sexual
selection  mate
chosen based on
“best” genes
– Mating call/dance
– Gifts
– Fighting
Mutation
• Random change in
genetic material
• May be harmful or
lethal
• Might ALSO be
beneficial
Natural Selection
• Acts to select the individuals
that are best adapted to their
environment
• Changes allele frequencies
and phenotype
• Stabilizing: neither extreme is
good  human baby weight
• Directional: influenced by
environment Peppered
Moth’s response to pollution
• Disruptive: both extremes
work for different habitats 
retains individuals expressing
extreme traits
Speciation
• Species diverge when
they are isolated
– Allopatric ( physical
barrier)
– Sympatric (no physical
barrier)
Rate of Speciation
• Gradualism
• Punctuated
Equilibrium