Download Ch 23 Ch 24 Evolution

Microevolution (Ch 23)
and
Macroevolution (Ch 24)
Gene Pools
A gene pool is the sum
of alleles within a
population
A population is a localized
group of organisms of the
same species
Microevolution
Changes occurring in a population
 Adaptations result in evolution

Macroevolution
Evolution
above the species level
 Origin of new taxonomic groups

Hardy-Weinberg Equilibrium
To assume Hardy-Weinberg equilibrium all of
the following must be true:
1. The population must be very large (no
sampling error/genetic drift)
2. There must be no mutation
3. There must be no natural selection
4. No migration between populations
5. Random mating
Hardy-Weinberg Equation
p=frequency of one allele (A); q=frequency of
the other allele(a);
p+q=1.0
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%)
p2 + 2pq + q2 = 1
Hardy Weinberg Equilibrium
Population of cats
n=100
16 white and 84 black
bb = white
B_ = black
Can we figure out the allelic frequencies of
individuals BB and Bb?
Using Hardy-Weinberg equation
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): 1 - 0.4 = 0.6
population:
100 cats
84 black, 16 white
How many of each
genotype?
p2=.36
BB
2pq=.48
Bb
q2=.16
bb
Hardy Weinberg Ex 1
 If
only 6% of the population displays
pale eyes (recessive gene e), what
is the frequency of genotype Ee in
this population?
q2 = 0.06 ---> q = 0.24
p + q = 1 ---> p = 0.76
Ee = 2pq = 2(0.76)(0.24) = 0.36
Hardy Weinberg Ex 2


If the statistics for people who have PKU
is 1 in 10,000, what percentage of the
US population carries the gene but does
not exhibit the disease?
q2 = 0.0001 ---> q = 0.01
p + q = 1 ---> p = 0.99
2pq = 2(0.99)(0.01) = 0.0198 or 1.98%
Genetic Drift
Genetic drift is random fluctuation in allele
frequency between generations.
A Genetic
Bottleneck is a
Form of Genetic
Drift
In a genetic bottleneck,
allele frequency is altered
due to a population crash.
Once again, small
bottlenecked
populations = big
effect.
Genetic Bottleneck – A Historical Case
A severe genetic bottleneck occurred in northern elephant
seals.
Other animals known to be affected by genetic bottlenecks
include the cheetah and both ancient and modern human
populations.
Founder Effect- new habitat
The South Atlantic island of Tristan da Cunha was colonized by 15 Britons
in 1814, one of them carrying an allele for retinitis pigmentosum. Among
their 240 descendents living on the island today, 4 are blind by the disease
and 9 others are carriers.
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

Migration (Gene Flow)
Mutations

Mutation creates
variation
a change in an organism’s
DNA (gametes; many
generations); original
source of genetic
variation (raw material for
natural selection)
Nonrandom Mating
Inbreeding
 assortive matingchoosing a mate with
either similarities or
differences (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!
Natural Selection
 differential
success in
reproduction;




climate change
food source availability
predators, parasites, diseases
toxins
 only form of
microevolution that adapts
a population to its
environment
• provides “fitness”
increase in the population
Genetic Variation
Polymorphism2 or more
distinct forms
(morphs) within
a single
population of
organisms
Geographic Variation-cline

differences in genetic
structure between
populations
Mutation and Sexual Recombination
-random changes
to DNA
errors in mitosis
& meiosis
environmental
damage
-Recombination
mixing of alleles
new combinations=
new phenotypes
Diploidy
 2nd
set of chromosomes
hides variations in the
heterozygote
Balanced polymorphism
heterozygote advantage
(hybrid vigor; i.e.,
malaria/sickle-cell anemia);
In reality there is little random
mating
Inbreeding can occur
within small or isolated
populations
 Mate selectionchoosing a mate similar
to one’s
self.(Homogamy)

Sickle-Cell Prevalence
Selection by
malaria
exposure
Evolutionary Fitness
Contribution an
individual makes to the
gene pool for the next
generation.
 The alleles of this
individual promotes the
survival or
reproductive success of
others that share the
same allele.

Modes of Selection
Stabilizing Selection- favors the
middle and eliminates the extremes in
a population
 Directional Selection- natural
selection or evolutionary changes in
the population
 Disruptive Selection- favors the two
extremes creating polymorphism.

Modes of Selection
Sexual Dimorphism
 Two
distinct
forms in the
sexes of
some species
Sexual Selection
Macroevolution: the origin of new
taxonomic groups Chapter 24
Speciation: the origin of new
species
 1- Anagenesis (linear
evolution): accumulation of
heritable changes
 2- Cladogenesis (branching
evolution): budding of new
species from a parent species
that continues to exist (basis
of biological diversity)

What is a species?

Biological species
concept: a population
whose members have
the potential to
interbreed and produce
viable, fertile offspring
Other Species’ Concepts

•
•

•

•

•

•
Biological Species Concept
Reproductive Isolation
Not necessarily easy to apply
Morphological Species Concept
Phenotypic differences
Paleontological Species Concept
Fossil species
Ecological Species Concept
Filling of ecological niches
Phylogenetic Species Concept
Evolutionary lineages/genetic history
Reproductive Isolation (isolation of gene pools)
Pre-zygotic barriers:
impede mating
between species or
hinder the fertilization
of the ova
 Habitat (snakes;
water/terrestrial)
 Behavioral (fireflies;
mate signaling)
 Temporal (salmon;
seasonal mating)
 Mechanical (flowers;
pollination anatomy)
 Gametic (frogs; egg coat
receptors)

Reproductive Isolation




Post-zygotic barriers:
fertilization occurs, but the hybrid
zygote does not develop into a
viable, fertile adult
Reduced hybrid viability (frogs;
zygotes fail to develop or reach
sexual maturity)
Reduced hybrid fertility (mule;
horse x donkey; cannot
backbreed)
Hybrid breakdown (cotton; 2nd
generation hybrids are sterile)
Modes of speciation (based on how gene
flow is interrupted)


Allopatric: populations
segregated by a
geographical barrier;
adaptive radiation –
diversification due to
habitat change
(Darwin’s finches)
Sympatric:
reproductively isolated
subpopulation in the
midst of its parent
population
Sympatric Speciation
Polyploidy-more than
2 paired
chromosomes
 Allopolyploidyinfertile hybrid
 Sexual selectionintraspecies
competition

Tempo of speciation


Gradualismspecies diverge
more and more as
they adapt
Punctuated
Equilibriumperiods of apparent
stability and then a
sudden change
Evolutionary Novelties



Exaptation- structures becomes better adapted for
another function- bird feathers originally kept the bird
warm but later were better suited for flight
Heterochromy- change in the rate of evolution- foot
development in salamanders
Paedomorphosis- retaining some juvenile
characteristics
Convergent Evolution
Analogies are products of
convergent evolution