Transcript Chapter 16: Evolution of Populations

Chapter 16: Evolution of
Populations
16.1 Genes and Variation
16.2 Evolution as Genetic Change
16.3 The Process of Speciation
Chapter 16 Concept Map
Pg. 393-394
Gene Pool
Relative Frequency
Different Types of Natural Selection
example
Stabilizing Selection
example
Directional Selection
example
Disruptive Selection
Genetic Equilibrium
Genetic Drift
Hardy-Weinberg
Principle
founder effect
Pg. 398-399
single gene trait
Pg. 395-401
polygenic trait
4
Chapter 16 Concept Map
Speciation
Geographic
Isolation
Reproduction
Isolation
17.4…. Macroevolution
example
adaptive radiation
gradualism
example
Pg. 435-440
example
extinction
Divergent
Temporal
Isolation
Behavorial
Isolation
example
example
Pg. 404-409
example
convergent evolution
punctuated equilibrium
example
coevolution
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Population Genetics
 Evolutionary thought
today is tightly linked
to genetics.
 Remember,
populations, not
individuals evolve.
 All the alleles in a
pop. added together
are called the gene
pool.
Blue People of Kentucky
Population Genetics
 The frequency that any one allele is seen
in the population is called the allele
frequency (relative frequency).
Is the frequency of the dominant
Huntington’s allele high?
 Is the frequency of
the dominant allele
causing 6 fingers high?

Population Genetics
 If the frequency of
the alleles doesn’t
change over time,
the population is at
genetic
equilibrium.
 Hardy-Weinberg
Principle

see page 401
Population Genetics
 When alleles are brought in and out
of a population due to migration of
individuals, it is called gene flow.
Population Genetics
 When isolated chance
events can alter gene
frequencies in a population
(therefore disrupting gene
equilibrium) you have what is
called genetic drift.



Common in small isolated
populations such as the Amish
of Lancaster, PA
Darwin’s finches (perhaps)
founder effect: change as a
result of migration
Population Genetics
 Sources of Genetic Variation:




Mutations
Gene Shuffling
Single gene trait
Polygenic trait
Population Genetics
 Types of selection: 

When natural selection of a trait favors the
average individuals in the pop. it is called
stabilizing selection.
Population Genetics
 Types of selection: 
When natural selection favors both extreme
phenotypes of a trait in a pop., it is called
disruptive selection.

Population Genetics
Types of selection: 
When natural selection favors one extreme
phenotype of a trait, it is called directional
selection.

Population Genetics
 Type of Selection??



Grey mice are preyed upon but black and white
mice are left alone?
Disruptive
The longer a giraffe’s neck gets the more food is
available, while short necked giraffes die of
starvation before they can reproduce?
Directional
A slow gazelle is easily caught by a cheetah, but
one too fast breaks its legs easily and is eaten by
hyenas??
Stabilizng
Population Genetics
 Artificial Selection: Selection
for traits that are determined
and monitored by man.

Ex. Breeding animals such as
dogs or cats.
 Sexual Selection: Selection
by one gender for another
gender.

Ex. Peacock feathers, body hair
disappearance in humans, walrus
tusks.
Speciation
 Speciation is
when a new species is
formed. This means
that the individuals in
the new species can no
longer produce
successful offspring
with the population
from which they came.
Speciation
 Geographic Isolation
can cause speciation over
long periods of time.


The seperated organisms are
adapting to different
environments and responding
differently.
Eventually if a mating is
attempted, they can no longer
produce successful offspring
with one another.
Speciation
 Reproductive Isolation is when a
population can no longer successfully
interbreed with its parent population (the
pop. it came from).

Reproduction if attempted will fail.
Ex. One group breeds
in the fall, one in the
spring and over time
the populations become
new species incapable
of interbreeding.
 Mating Calls
 Courtship rituals differ

Speciation
 Temporal Isolation:


Two or more species reproduce at
different times
Example: orchid in the rainforest
Speciation
 Changes in chromosome number
can cause speciation.
 Some cases of polyploidy (more
common in plants) produce
individuals that can only mate with
other polyploids in a pop.
17.4 Speciation
 Can occur rapidly
Punctuated Equilibrium
 Gould

 Can occur very slowly
Gradualism
 Darwin
 see page 439

17.4 Patterns of Evolution
 Adaptive Radiation: When an
ancestral species evolves into
several different species, each filling
a specific niche.
Darwin’s finches
 Hawaiian Honeycreepers
(p. 406 &436).

17.4 Patterns of Evolution
 Divergent Evolution: Species that
once were similar or closely related
become very different.

New Species are very different from
each other.

Ex. Adaptive Radiation
17.4 Patterns of Evolution
 Convergent
Evolution: Unrelated
species that live in
similar environments
evolve the same
adaptations in order to
survive.


Ex. Tasmanian Wolf and
North American Wolf.
P. 437
Patterns of Evolution
 Coevolution: the
process by which two
species evolve in
response to changes in
each other over time.


Example: flowering plants
and their pollinator
Page 437
http://biology.clc.uc.edu/courses/bio303/coe
volution.htm
17.4 Note
 Common genetic occurrences we
have studied such as polyploidy,
crossing over, and point mutations can
provide the genetic basis for evolution.
Although these genetic changes are not
evolution themselves, they can begin the
long process of evolution by affecting
one individual in a population in a
positive way. But only if the trait is
passed on, and on, and on…