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Chapter 16 EVOLUTION OF POPULATIONS
Powerpoint NOTES
16-1: Genetic equilibrium

Population genetics: study of _________________ from a ______________point of view

Basically how __________________________________________________

But what is a population?
______________________________________________________________
Sources of Genetic Variation

Mutations: any change in ________________________________

R________________ mistakes

R___________________/e_______________________causes

Recombination: reshuffling of __________________

Random pairing of _________________
Bell Curve

Many traits in nature show trends like this
Label the
X and Y axis

Number of __________________________
produced depends on how many ___________
control that trait

Single gene traits- have ______ alleles

Two distinct p______________________
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Polygenic traits- controlled by _________________ genes

Results in ____________ phenotypes

Gene pool- all _________, including all different alleles, that are present in a ________________

frequency (of an allele)- number of times ____________ occur in a ____________________
o

Expressed as a p______________
Genetic definition of evolution?
o
Change in __________________________ of alleles in a population over time
Phenotype Frequency

How often a specific ____________________________ is observed in a population
o

Can be written m ________________________
Frequency =
# indiv. w/a particular phenotype
total # of indiv. in population
Hardy-Weinberg Equilibrium

When evolution is _______ occurring

Allele frequencies _______________________

In order for evolution to not occur, certain conditions must be met.
Evolution vs. Genetic Equilibrium
Hardy-Weinberg principle = Genetic ___________________
1. Random Mating – Equal opportunity to __________________________________________
2. Large Population – Genetic Drift does not affect ____________________________________
3. No Movement into or out of Population – The gene pool must be kept together (no ______
alleles)
4. No Mutations – Mutations cause new forms of _______________ changing the frequency
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5. No Natural Selection – All genotypes must have equal probability of ______________________
Allele frequency equation


p+q=1
p = frequency of ___________________ allele
q = frequency of _________________ allele
Together, they make 100% of alleles for a gene in that population
Genotypic frequency equation
p2 + 2pq + q2 = 1
p2 = h_______________ dominant frequency
2pq = h_______________ frequency
q2 = h______________ recessive frequency
Disruption of Genetic Equilibrium

M____________________

Occur at a relatively _________________ rate over time

Can be sped up when exposed to m__________________

Gene flow: process of genes moving from _________________________ to another

Immigration: moving ___________ a population

Emigration: moving ___________ of a population
_____________________________________________________________________________________
Genetic Drift

Alleles can become __________ by chance

Over time a series of ________________ occurrences can cause an alleles to become
________________ in a population

Effects of genetic drift are more dramatic with ____________ population size

Founder effect: change in allele frequencies as a result of m_______________ of a small
s__________________ of a population
Sample of
Original Population
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Founding Population A
Descendants
Founding Population B
_____________________________________________________________________________________
Nonrandom Mating


Sexual selection: tendency of individuals to choose a ___________ with certain ____________.
Common in birds
o Peacock display
o Tropical birds of paradise - Papua New Guinea
o The amazing Lyrebird – Australia
_____________________________________________________________________________________
Natural Selection


Natural selection on single gene traits can lead to changes in _____________________________
Natural selection on polygenic traits
o 3 possible effects
 D______________ selection
 S_____________ selection
 D_______________ selection
_____________________________________________________________________________________
Directional Selection
 When individuals at one end of curve have
_____________________________
than individuals in the middle or the other end
Stabilizing Selection
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 When individuals near the ___________ have higher fitness than the individuals at
____________________
_____________________________________________________________________________
Disruptive Selection
 When individuals at ___________ and _____________
ends have higher fitness than individuals near the
____________
_____________________________________________________________________________________
16-3 Formation of Species

As new species evolve, populations become reproductively isolated from each other

Reproductive isolation: when two members of populations cannot interbreed and produce
fertile offspring

Separate gene pools
_____________________________________________________________________________________
Isolation Mechanisms
Geographic Isolation:
 separation of animals in a specific region
- formation of river, canyon, mountain
_____________________________________________________________________________________
Behavioral Isolation:

differences in courtship or reproductive behaviors
 meadowlark songs
Temporal isolation:
-two or more species reproduce at different times
-orchids
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Formation of Species
Allopatric speciation: when species arise from geographic isolation
Different places
Reproductive Isolation
Prezygotic isolation: premating isolation
Species may live
in different places
Reproduce at different times
Have different mating behaviors
Postzygotic isolation: postmating isolation
Hybrids may be weak
Hybrids may be sterile
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Sympatric Speciation
 when two subpopulations become isolated while living in the same area
Rates of Speciation
Gradualism: speciation at gradual and regular rate
Punctuated equilibrium: periods of sudden,
rapid change followed by periods of little change