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Week 5!!
Get ready for entrance quiz
Labs—Discussions and graphs
need work
Evolution evidence:
Biogeography
• Geographical
distribution of species
• Examples:
Islands vs. Mainland
Australia
Continents
Evolution evidence:
The Fossil Record
• Succession of forms
over time
• Transitional links
• Vertebrate descent
Fossil Record
2006 Fossil Discovery of Early Tetrapod
• Tiktaalik
– “missing link” from sea to land animals
Evolution evidence:
Comparative Anatomy
• Homologous
structures
(homology)
• Descent from a
common ancestor
Homologous structures
•
•
•
•
Similar structure
Similar development
Different functions
Evidence of close
evolutionary relationship
– recent common ancestor
Homologous structures
spines
leaves
succulent leaves
needles
colored leaves
tendrils
Analogous structures
 Separate evolution of structures
similar functions
 similar external form
 different internal structure & development
 different origin
 no evolutionary relationship

Don’t be fooled
by their looks!
Solving a similar problem with a similar solution
Vestigial organs
• Modern animals may have structures that serve
little or no function
– remnants of structures that were functional in
ancestral species
– deleterious mutations accumulate in genes for noncritical structures without reducing fitness
• snakes & whales — remains of pelvis & leg bones of
walking ancestors
• eyes on blind cave fish
• human tail bone
Dispatch
1) Compare analogous to homologous
structures
2) What are 3 pieces of evidence that
whales evolved from land mammals?
3) Give 2 examples of vestigial structures.
Evolution evidence:
Comparative Embryology
• Pharyngeal
pouches, ‘tails’ as
embryos
Evolution evidence:
Molecular Biology
• Similarities in
DNA, proteins,
genes, and gene
products
• Common genetic
code
Closely related species have
sequences that are more similar
than distantly related species
 DNA & proteins are a molecular
record of evolutionary relationships
Building “family” trees
Closely related species (branches) share same line of
descent until their divergence from a common ancestor
Artificial selection
• Artificial breeding can use variations in
populations to create vastly different “breeds” &
“varieties”
“descendants” of wild mustard
“descendants” of the wolf
Natural selection in action
• Insecticide &
drug resistance
– insecticide didn’t
kill all individuals
– resistant survivors
reproduce
– resistance is inherited
– insecticide becomes less
& less effective
Final words…...
• “Absence of evidence
is not evidence of
absence.”
Evolution on a micro level
• Looking at alleles
• Looking at the DNA
• DARWIN DIDN”T KNOW DNA
Get a bottle and colored sticks
Microevolution, II: type of genetic
drift
• The Bottleneck
Effect: type of genetic
drift resulting from a
reduction in population
(natural disaster) such
that the surviving
population is no longer
genetically
representative of the
original population
Microevolution, I
• A change in the gene
pool of a population
over a succession of
generations
• 1- Genetic drift:
changes in the gene
pool of a small
population due to
chance (usually
reduces genetic
variability)
Chapter 23~
• Chapter 23~
The Evolution of
Populations
Population genetics
•
•
•
•
•
•
Population:
a localized group of individuals
belonging to the same species
Species:
a group of populations whose
individuals have the potential to
interbreed and produce fertile offspring
Gene pool:
the total aggregate of genes in a
population at any one time
Population genetics:
the study of genetic changes in
populations
Modern synthesis/neo-Darwinism
“Individuals are selected, but
populations evolve.”
Conservation issues
Peregrine Falcon
• Bottlenecking is an important
concept in conservation
biology of endangered
species
– loss of alleles from gene pool
– reduces variation
– reduces adaptability
Breeding programs must
consciously outcross
Golden Lion
Tamarin
Microevolution, III type of genetic
• Founder Effect:
a cause of genetic drift
attributable to
colonization by a limited
number of individuals
from a parent population
– just by chance some rare
alleles may
be at high frequency;
others may be missing
– skew the gene pool of
new population
• human populations
that
started from small
group
of colonists
• example:
drift
Dispatch
1) Compare and contrast:
-founder effect
-genetic drift
-bottle neck effect
2) Give 3 deadlines for October
Microevolution, IV
• 2- Gene Flow:
genetic exchange due
to the migration of fertile
individuals or gametes
between populations
(reduces differences
between populations)
• seed & pollen distribution by
wind & insect
• migration of animals
Microevolution, V
• 3- Mutations: a
change in an
organism’s DNA
(gametes; many
generations); original
source of genetic
variation (raw material
for natural selection)
• Mutation creates
variation
Microevolution, VI
• 4- Nonrandom
mating:
• Sexual selection
• inbreeding and
assortive mating (both
shift frequencies of
different genotypes)
Sexual selection
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
It’s FEMALE CHOICE, baby!
Microevolution, VII
5.NaturalSelection
• differential success
in reproduction;
• climate change
• food source availability
• predators, parasites,
diseases
• toxins
•
only form of microevolution
that adapts a population to
its environment
• combinations of alleles
that provide “fitness”
increase in the population
Natural Selection
• Selection acts on any trait that affects
survival or reproduction
– predation selection
– physiological selection
– sexual selection
Variation & natural selection
• Variation is the raw material for natural
selection
– there have to be differences within population
– some individuals must be more fit than others
– random changes to DNA
• errors in mitosis & meiosis
• environmental damage
Beak depth
•
Where does Variation come
from?
Mutation
Dry year
Dry year
1977
• Sex
Wet year
Dry year
1980
1982
1984
– mixing of alleles
• recombination of alleles
– new arrangements in every offspring
• new combinations = new phenotypes
– spreads variation
• offspring inherit traits from parent
Beak depth of
offspring (mm)
11
10
9
8
Medium ground finch
8
9
10
11
Mean beak depth of parents (mm)
Population variation
• Polymorphism:
coexistence of 2 or
more distinct forms of
individuals (morphs)
within the same
population
• Geographical
variation: differences
in genetic structure
between populations
(cline)
Variation preservation
• Prevention of natural selection’s
reduction of variation
• Diploidy
2nd set of chromosomes hides
variation in the heterozygote
• Balanced polymorphism
1heterozygote advantage (hybrid
vigor; i.e., malaria/sickle-cell
anemia);
2- frequency dependent selection
(survival & reproduction of any 1
morph declines if it becomes too
common; i.e., parasite/host)
Natural selection
• Fitness:
contribution an
individual makes
to the gene pool
of the next
generation
• 3 types:
• A. Directional
• B. Diversifying
• C. Stabilizing
Effects of Selection
• Changes in the average trait of a population
DIRECTIONAL
SELECTION
giraffe neck
horse size
STABILIZING
SELECTION
human birth weight
DISRUPTIVE
SELECTION
rock pocket mice
Sexual selection
• Sexual dimorphism:
secondary sex
characteristic distinction
• Sexual selection:
selection towards
secondary sex
characteristics that leads
to sexual dimorphism
Any Questions??
Hardy-Weinberg Theorem
•
•
Serves as a model for the genetic
structure of a nonevolving population
(equilibrium)
Evolution = change in allele frequencies
in a population
– hypothetical: what conditions not
would cause allele frequencies to
change?
– non-evolving population
REMOVE all agents of
evolutionary change
1. very large population size (no
genetic drift)
2. no migration (no gene flow in
or out)
3. no mutation (no genetic
change)
4. random mating (no sexual
selection)
5. no natural selection
(everyone is equally fit)
Hardy-Weinberg Equation
• p=frequency of one allele (A);
other allele (a);
p+q=1.0
q=frequency of the
(p=1-q & q=1-p)
• p2=frequency of AA genotype;
2pq=frequency of Aa genotype;
q2=frequency of aa genotype;
•
frequencies of all individuals must add to 1
(100%), so:
G.H. Hardy
2
mathematician
p + 2pqW.+Weinberg
q2 = 1
physician
Using Hardy-Weinberg equation
population:
100 cats
84 black, 16 white
How many of each
genotype?
p2=.36
BB
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): 1 - 0.4 = 0.6
2pq=.48
Bb
q2=.16
bb
What assume
Must
are the population
genotype frequencies?
is in H-W equilibrium!
Hardy Problem
•
Calculate q2 Count the individuals that are homozygous recessive in the
illustration above. Calculate the percent of the total population they
represent. This is q2.
Q2=4/16=0.25
Calculate q
Q=0.5
p + q = l. You know q, so what is p, the frequency of the dominant allele?
P=0.5
Find 2pq
2pq = 2(0.5) (0.5) = 0.5 , so 50% of the population is heterozygous.
Problem 1
• In a certain population of 1000 fruit flies, 640
have red eyes while the remainder have sepia
eyes. The sepia eye trait is recessive to red
eyes. How many individuals would you expect to
be homozygous for red eye color? Hint: The first
step is always to calculate q2! Start by
determining the number of fruit flies that are
homozygous recessive. If you need help doing
the calculation, look back at the Hardy-Weinberg
equation.
Problem 2
• The Hardy-Weinberg equation is useful for
predicting the percent of a human population
that may be heterozygous carriers of recessive
alleles for certain genetic diseases.
Phenylketonuria (PKU) is a human metabolic
disorder that results in mental retardation if it is
untreated in infancy. In the United States, one
out of approximately 10,000 babies is born with
the disorder. Approximately what percent of the
population are heterozygous carriers of the
recessive PKU allele?