Evolution Continued
Chapter 16: pgs 392 – 415
Chapter 17: pgs 416 - 445
Variation & Gene Pools
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Gene Pool- consists of all genes, including all
the different alleles, present in a population
Allele- One of a number of different forms of a
gene
Relative Frequency- The number of times that
the allele occurs in a gene pool
– Has nothing to do with the gene being
dominant or recessive
– Example: Mice being black or brown
Evolution- any change in the relative frequency
of alleles in a population
Genetic Variation
 Recall-
Genetics is a game of
chance
 Certain Individuals in Small
populations pass on particular
alleles
–Overtime this can cause alleles to
appear frequent
Sources of Genetic Variation
 Mutations
of DNA
-Any change in a sequence
– Either by mistake in replication OR
radiation/chemical
 Gene
Shuffling- The different
combination that occur when two
organisms mate
– You look like a combination of both
parents
– Many different combinations
Natural Selection
 Natural
selection on single-gene
traits can lead to changes in allele
frequencies and thus evolution
– Single-gene trait- A single gene that has
two alleles (example: Different species
colors)
 Mice
that stand out get eaten faster
 Therefore, Less Likely to survive to
reproduce
Natural Selection Continued
 Polygenic
Traits- Traits controlled by
two or more genes (example:
height)
 Directional Selection- Characteristics
of one species is favored Example:
Beak Size
– Larger VS Smaller (Food Shortage)
 Stabilizing
Selection- Human baby
birth weight
– Smaller babies = less healthy
– Larger= birth problems
Testing Natural Selection in Nature

Variation
– When same species has different anatomical features
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Color, size, beaks, total mass
– Example: Finches
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Natural Selection
– Rainy Season VS Dry Season
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Rainy = Numerous Sources of Food
Dry = Depleted/Scare sources
These differences create Natural Selection
Rapid Evolution
– Once differences occur, species can change features
relatively quickly (Each breeding season beaks get
bigger
Genetic Drift
 In
small populations alleles can
become more or less common
– Controlled by probability
 Occurs
when a random change of
traits occur over time
– Such as animals colonizing a new
habitat
Genetic Equilibrium
 Hardy-Weinberg
Principle
– Allele frequencies stay constant unless
one or more factors cause frequencies
to change
5
required conditions:
– Random mating
– Very large population
– No immigration/emigration
– No mutations
– No natural selection
Process of Speciation
 Isolating
mechanisms
– As new species evolve, populations
become isolated
– Behavioral Isolation
2
species capable of mating, but different courtship
– Example: Different mating songs in birds
– Geographic Isolation
2
populations separated by geographic barriers
– Example: Squirrels around Grand Canyon
 One side has gray & other is black
– Temporal Isolation
 Two
or more species breed at different times
– Example: Plants releasing pollen on different
days
Ch. 17 History of Life
 Paleontologists
– Scientists who study fossils
 Fossil
Record
– Grouping of organisms based on
characteristics
– Provides evidence about the history of
life on Earth
– Shows how different groups have
changed over time
 Extinction
– When species die out
– More than 99% of all species are
already extinct
Patterns of Evolution

Adaptive Radiation
– Process where species evolve into new
and divers forms and create new
species
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Darwin’s finches!
Convergent Evolution
– Occurs when two entirely different,
unrelated species, develop similar
characteristics
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Examples: fish, dolphins, sea lions &
penguins
Patterns of Evolution Cont.
 Coevolution
– A process where two species who
interact with each other evolve together
 Example:
 Punctuated
Flowers & Pollinators (bees)
Equilibrium
– Scientists use this to describe patterns
of long stable periods interrupted by
periods of rapid change in the fossil
record
 Finches
moving from island to island
– Trying to fill available niches