MICROEVOLUTION VS.
MACROEVOLUTION
• Microevolution: survival through the
inheritance of favorable characteristics
– mutations
– selection
• Macroevolution: progression of biodiversity
through geological time
– speciation
– extinction
MICROEVOLUTION
Evolutionary Mechanisms
Types of Natural Selection
Hardy-Weinberg Equilibrium
WHAT IS MICROEVOLUTION?
• Traces generational changes in a
population of organisms
• Changes eh?
– Allelic frequency changes within a
gene pool!
•
WHAT LEADS TO CHANGES
IN THE GENE POOL OF A
POPULATION?
• SMALL POPULATION SIZE
(small pop 
frequencies)
toss a coin to prove it.
MECHANISMS OF
EVOLUTION
• GENETIC DRIFT
(random/chance events that change the
gene pool of a small population)
examples:
natural disasters
2 TYPES OF GENETIC DRIFT
MECHANISMS
• Genetic Bottleneck
dramatic decrease in pop size
due to :
catastrophes
predation
disease, etc.
• Founder Effect
migration leads to changes in allele
frequencies from population of origin
WHAT ELSE CAUSES GENE
POOL CHANGES ?
• GENE FLOW
immigration
emigration
EX OF GENE FLOW IN
HUMANS
• Frequency of Rh- allele among
Africans:
63%
• Frequency of Rh- allele among
African-Americans
45%
• Frequency of Rh- allele among White
European population
• MUTATIONS
may produce a selective advantage
may produce deleterious effects
may be harmless
• NATURAL SELECTION!
increases/decreases allele frequencies
due to environmental impact.
Ex: English Peppered Moths
• NON-RANDOM MATING
individuals choose based upon traits
(vertebrates)
individuals “choose” based upon
physical proximity
(invertebrates)
OTHER FORMS OF NONRANDOM MATING:
•
INBREEDING
– Proximity issues
•
SEXUAL SELECTION:
1. Male competition:
# offspring  fitness
2. Female choice:
quality offspring  fitness
SEXUAL
SELECTION
Picky females, show-off males…
MICROEVOLUTION REVIEW
• Changes in the GENE POOL!
• Caused by:
– Gene Flow
– Natural Selection
– Mutations
– Non-Random Mating
• Sexual Selection
• Inbreeding
THE SIGNIFICANCE OF
SELECTION
• Selection increases the adaptive qualities
of a population for the environment in
which it lives.
Types of Selection:
Natural Selection
determined by phenotype
selection toward phenotypes that
improve fitness
SUBDIVISIONS OF NATURAL
SELECTION…
Stabilizing Selection
Eliminates individuals with extreme traits.
Results in decreased variation
Directional Selection
Favors traits at ONE extreme
ex: resistance to insecticides
DIRECTIONAL SELECTION
Disruptive Selection
Selection toward BOTH extremes. Extreme
traits are favored, common traits are NOT!
Results in major divisions in population!
What might result?
DISRUPTIVE SELECTION
ARTIFICIAL
SELECTION
Directional selection determined by humans
CAUSES OF VARIATION
• Mutation is the ultimate source
of variation
• Two major types of mutations:
–Gene mutations
–Chromosome mutations
GENE MUTATIONS
Addition / Insertion
Deletion
Substitution
Inversion
SPECIFIC EXAMPLES OF
MUTATIONS
• Gene mutations
–PKU (phenylketonuria)
–CF (cystic fibrosis)
• Chromosome mutation
–Klinefelter syndrome (male with
47,XXY karyotype)
ONCE MUTATIONS HAVE
ARISEN, FURTHER VARIATION
RESULTS FROM:
• Recombination
of alleles during
meiosis
• Recombination
of alleles during
ONCE GENETIC VARIATION
HAS ARISEN, THERE IS
ALSO PHENOTYPIC
VARIATION.
• Recall that, according to
Darwin’s Theory, due to
competition within
populations, there is …
Differential Reproduction
GREAT EXAMPLE OF
DIFFERENTIAL
REPRODUCTION OF
SELECTED PHENOTYPES:
ULTIMATE RESULT OF
EVOLUTION
Change in the genetic
composition (gene pool) of
a population.
RELATED CAUSES OF
GENETIC VARIATION
Sexual Reproduction!
• Diploidy
• Outbreeding
MINORITY ADVANTAGE…
• 50/50 Sex Ratio
• Predation (more common phenotype
preferred by predator)
• The Lefty Hypothesis
10-15 % general population
>50% contact sports (esp. males)
REPRODUCTIVE ISOLATION
Prezygotic
• Temporal
isolation
• Behavioral
isolation
• Mechanical
isolation
• Ecological
Postzygotic
• Hybrid
inviability
• Hybrid sterility
• Hybrid
breakdown
ALLOPATRIC SPECIATION
SYMPATRIC SPECIATION
GRADUALISM
Species A
evolves to
become
species B.
LONG,
GRADUAL
process!
PUNCTUATED EQUILIBRIUM
• Evolution is
Slow with brief
periods of rapid
development of
new species.
THE HARDY WEINBERG LAW
• If allele frequencies for a population do
not change…
NO EVOLUTION IS OCCURRING!
• Genetic Equilibrium
• Hardy Weinberg Equilibrium
GENETIC EQUILIBRIUM
OCCURS ONLY IF THERE IS…
1.A large breeding
population
2.Random mating
3.No change in allelic
frequency due to mutation
4.No immigration or
emigration
EQUILIBRIUM REQUIRES…
• Large Population Size
(laws of probability must apply)
• Isolation of Population
(no immigration/emigration to/from
other populations)
• NO MUTATIONS ALLOWED!
• NO NATURAL SELECTION !
all traits must be selectively neutral
• Mating Must Be RANDOM
equal probabilities of mating btwn
IS HW EQUILIBRIUM
POSSIBLE?
• YES ?
/ NO ?
• WHY / WHY NOT??
• http://zoology.okstate.edu/zoo_lrc/biol1114
/tutorials/Flash/life4e_15-6-OSU.swf
THE HARDY-WEINBERG
EQUATION
•
Given one locus with two alleles (A,a) the
frequency of either allele is described by
a number from zero to one:
allele absent from pop  freq = 0
same allele in all indiv in pop 
freq = 1
WHAT IF BOTH ALLELES ARE
PRESENT IN A POPULATION?
• Frequency of both alleles is equal to
p+q=1
[p = dominant allele (A)]
[q = recessive allele (a)]
• Knowing the frequency of one allele allows
for the calculation of the other…
p = 1- q ; q = 1 - p
• If p+q=1,
then (p+q)2 = 1.
Expand it and get…
p
2
+ 2pq
+
2
q
= 1
WHAT DOES IT ALL MEAN
GENOTYPICALLY?
p2
= frequency of AA
2pq = frequency of Aa
q2
= frequency of aa
PROBLEM 1
• In pigs, the allele for
black coat (b) is
recessive to the allele for
pink coat (B).
WHAT % OF PIGS ARE
HETEROZYGOUS FOR PINK
COAT?
PROBLEM 2
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?
PROBLEM 3
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?
POPULATION IS BORN
WITH A SEVERE FORM OF
SICKLE-CELL ANEMIA (SS),
WHAT PERCENTAGE OF
THE POPULATION WILL BE
MORE RESISTANT TO
MALARIA BECAUSE THEY
ARE HETEROZYGOUS(SS)
FOR THE SICKLE-CELL
GENE?