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Warm Up
•Which undergoes
evolution …
• Individuals or populations?
What the…….
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Chapter 16
Evolution of populations
Variation and gene pools
• Gene pool – consists of all genes
• Genetic variation – 2 main sources
• Mutation
–Change in sequence of DNA
• Crossing over
–Occurs during production of
gametes
Process of speciation
• As new species evolve,
populations become
reproductively isolated
from each other by three
main concepts
– Behavioral isolation
– Geographic isolation
– Temporal isolation
What is reproductive isolation?
• When members of two populations
cannot interbreed and produce fertile
offspring….
– Reproductive isolation occurs
• Now have separate gene pools
• Respond to natural selection
and genetic drift as different
units.
Behavioral Isolation – leads to
reproductive isolation
Very common mechanism
used to keep closely related
animals from interbreeding
Include differences in …
•courtship behavior
•chemical signals
•mating calls
•
Geographic Isolation – leads to reproductive
isolation
Two populations separated by
geographic barrier
– Rivers
– Mountains
– Bodies of water
• Natural selection now works
separately on both populations
• Apert and Kaibab squirrels
– Separated by Colorado river
aprox. 10,000 yrs ago.
Temporal Isolation – leads to
reproductive isolation
• 2 or more species reproduce at
different times
– Leads to speciation because
• Unlikely to reproduce with
each other
• Then may become separate
species
Warm Up
• ________________ is when two species
breed at different times.
Evolution of Populations
Evolution of Populations
Part 2
Part 2
Natural Selection on Polygenic
Traits
Directional
Stabilizing
Disruptive
•
Natural Selection on Polygenic
Traits
Directional – whole populations range
shifts
– Ex. Average height of humans is taller now
• Stabilizing - whole populations range gets
larger
• Disruptive – populations range gets
disrupted
– Ex. If disease struck humans that only
affected middle aged people.
Testing natural selection in
nature
• Natural selection
– Individuals with different traits have
different chances of survival during a
environmental event
• Galapagos finches
–When food scarce on island due to
drought, finches with largest beaks
most likely to survive
Rapid Evolution
Natural selection takes place
frequently and sometimes very
rapidly
– Ex. Galapagos finches
• Due to drought, next
generation of finches had
larger beaks than did
generation before
selection had occurred.
• Finches had evolved
rapidly due to natural
selection
Speciation in Darwin’s finches
• Founders arrive
– Some species foreign to area arrive
• Separation in population
– Some from founding group get isolated
• Changes in gene pool occur
– Due to separation and natural selection
• Reproductive isolation
– Evolved to point that neither population, if came in contact would/could
reproduce
• Ecological Competition
– If both populations regroup in certain area, competition for similar food
sources will occur
• Continued Evolution
– Process continues on
Hardy – Weinberger formula
• The Hardy-Weinberg formula allows scientists to
determine whether evolution has occurred.
p 2 = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q 2 = frequency of aa (homozygous recessive)
Hardy – Weinberger formula
• 5 conditions are required to maintain genetic equilibrium
1. Random mating
2. Large population
3. No movement in or out of population
4.No mutations
5. No natural selection
What is the chance this happens in the wild
Warm Up
What type of isolating mechanism is this?