evolution any change in the genetic constitution of a population of organisms. –changes of lesser...
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Evolution
• Any change in the genetic constitution of a population of organisms.
– Changes of lesser magnitude are called microevolution.
– Changes at or near the upper extreme are called macroevolution
Table 12.1Page 194
Individuals, and their alleles, move into and out of populations; the physical flow counters the effects of the other microevolutionary processes
Gene flow
Random fluctuation in allele frequencies over time due to chance occurrences alone
Genetic drift
Change or stabilization of allele frequencies; an outcome of differences in survival and reproduction among variant individuals of a population
Natural selection
A heritable change in DNAMutation
Table 12.1 Microevolutionary Processes
phenotypes of original population
phenotype of island population
A seabird carries a few seeds, stuck to its feathers, from the mainland to a remote oceanic island.
Development of a Theory
• Lyell– Gradualism: Geological changes occur
over millions of years.
• Lamarck– Acquired characteristics are inherited
• Darwin and Wallace – Natural Selection
Natural Selection
• Four Mechanisms of Natural Selection– More born than can survive
• Not everyone makes it
– Variability in the population• Genetic differences
– Heritability of traits• The differences are inherited
– Fitness• Some produce more offspring than others
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Beak of the Finch
Geospiza conirostris G. scandens
Certhidea olivacae Camarhynchys pallidus
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490 AA butterfliesdark-blue wings
420 Aa butterfliesmedium-blue wings
90 aa butterflieswhite wings
Starting population Next generation
490 AA butterfliesdark-blue wings
420 Aa butterfliesmedium-blue wings
90 aa butterflieswhite wings
Next generation
490 AA butterfliesdark-blue wings
420 Aa butterfliesmedium-blue wings
90 aa butterflieswhite wings
Range of values at time 3
Nu
mb
er o
f in
div
idu
als
Range of values at time 2
Nu
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er o
f in
div
idu
als
Directional selection
Range of values at time 1
Nu
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f in
div
idu
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Range of values at time 1
Nu
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f in
div
idu
als
Range of values at time 2
Nu
mb
er o
f in
div
idu
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Stabilizing Selection
Range of values at time 3
Nu
mb
er o
f in
div
idu
als
Range of values at time 1
Nu
mb
er o
f in
div
idu
als
Disruptive Selection
Range of values at time 3
Nu
mb
er o
f in
div
idu
als
Range of values at time 2
Nu
mb
er o
f in
div
idu
als
per
cen
t o
f p
op
ula
tio
n20
15
10
5
1 2 3 4 5 6 7 8 9 10 11
birth weight (pounds)
100
70
50
30
20
10
5
3
2
percen
t mo
rtality