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Chapter 16 EVOLUTION &
SPECIATION
VOCABULARY REVIEW
• ALLELE – ONE OF A NUMBER OF DIFFERENT FORMS
OF A TRAIT
• GENE – THE DNA SEQUENCE FOR A TRAIT
• GENOTYPE – REPRESENTATION OF THE GENE
• PHENOTYPE – PHYSICAL CHAR. OF AN ORGANISM
• VARIATION – DIFFERENCES /DIVERSITY
• Example - Blood type has 3 alleles (A, B, and O); it
has 6 genotypes; providing a variation of 4 blood
types
NEW VOCABULARY
• POPULATION – GROUP OF
INDIVIDUALS OF SAME SPECIES
THAT INTERBREED
• GENE POOL – COMMON GROUP OF
ALL GENES PRESENT IN A
POPULATION
Gene Pool
Combined genetic
info. of all
members
Allele frequency is
# of times
alleles occur
(has nothing to do
with dominant or
recessive!)
Variation in Populations
2 processes can
lead to this:
Mutations change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
Genetic Drift changes populations…….
• Random change in allele
frequency causes an allele to
become more or less common
• Founder Effect:
one cause of genetic
drift
• Gene Flow:
genetic exchange
due to the
migration of fertile
individuals or
gametes between
populations
(reduces
differences
between
populations)
• Nonrandom mating: inbreeding and
selective breeding (both shift
frequencies of different genotypes)
• Natural Selection:
adapts a
population to its
environment
Sexual selection
• Sexual
dimorphism
• Sexual selection:
selection towards
secondary sex
characteristics
that leads to
sexual
dimorphism
Evolution of Populations
• change in
relative
frequency of
alleles
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
mutation!
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
Generation 4: 0.12 not resistant
0.88 resistant
WHY SHOULD WE BE WORRIED ABOUT RESISTANCE?
http://evolution.berkeley.edu/evolibrary/home.php
Phenotype Expression
• Depends on
how many
genes control
that trait
Single-Gene vs. Polygenic Traits
Single-Gene:
2 Distinct Phenotypes (EG: tongue rolling)
Polygenic:
Many Phenotypes
Allele Frequencies
Natural Selection
Single Gene
Traits
Genetic Drift
Polygenic
Traits
Directional
Selection
Stabilizing Selection
Disruptive Selection
Peccaries are
great
predators of
cacti
= original cactus
population
= population after
introduction of
peccaries
•What type of selection occurred
with the peppered moth?
What type of selection is human
birth weight?
Changes in populations due to geographic
factors
Environmentslight differences may influence direction of natural selection
H – allele for normal
hemoglobin
S – allele for sickle
hemoglobin
Genotypes:
HH
Normal
blood, no
malaria
resistance
HS
SS
Mostly normal,
malaria
resistance
All sickle, will
die young
Distribution of
malaria
Distribution of sickle
cell trait
Think about it:
1. What type of selection is the
malarial resistance in Africa?
2. What would happen to the sickle
cell allele if malaria were
eradicated? (look at how
common the allele is in other
parts of the world!)
3. So what might be the type of
selection for the sickle cell
allele in Europe?
Conditions needed for Genetic
Equilibrium
SPECIATION
• FORMATION OF NEW SPECIES
• AS NEW SPECIES EVOVLVE,
POPULATIONS BECOME
REPRODUCTIVELY ISOLATED
2 NEW POPULATIONS CANNOT INTERBREED
& PRODUCE FERTILE OFFSPRING.
3 ISOLATING MECHANISMS……..
1. BEHAVIORAL ISOLATION- capable of breeding but
have differences in courtship rituals (ex. eastern and
western meadowlarks)
2. GEOGRAPHICAL ISOLATION – separated by
geographic barriers like rivers, mountains, or bodies
of water (ex. Albert and Kaibab squirrels)
3. TEMPORAL ISOLATION – 2 or more species
reproduce at different times. (ex. Orchids)
Tigon
Offspring are infertile.
Liger
Separated both
geographically and
ecologically.
Fig. 23.6
Four species of leopard frogs: differ in their
mating calls. Hybrids do not live.
Learning check: What type of isolation is this?
These squirrels live on opposite sides of the Grand
Canyon. This is an example of ________ isolation.
Hawaiian Honeycreepers
An example of adaptive radiation –
these species all diverged from a
common ancestor (founder species)
FOUNDER SPECIES
SPECIATION IN DARWIN’S
FINCHES
• SPECIAITON IN THE GALAPAGOS
FINCHES OCCURRED BY:
- FOUNDING OF A NEW POPULATION,
- GEOGRAPHIC ISOLATION which led to –
REPRODUCTIVE ISOLATION and
CHANGES IN THE NEW POPULATION’S
GENE POOL due to COMPETITION.
Patterns of Macroevolution
1.Adaptive Radiation
2.Convergent evolution
3.Coevolution
4.Extinction
1. Adaptive Radiation
Flying
Squirrel
Sugar
Glider
Marsupial Mammals
2. Convergent
Evolution
and
Analogous
Structures
Placental mammals
Mammalia
Rat like
common
ancestor
Think about it:
What are other examples of convergent
evolution?
3. COEVOLUTION
4. Extinction
•Usually
coincides with
global climate
change
•99% off all
species that
ever lived are
now extinct