Download Microevolution

Schedule Change!

Film and activity next Friday instead of
Lab 8. (No need to print/read the lab
before class.)
Today: Thinking About Darwinian
Evolution
Part 1:
Darwin’s
Theory
What is evolution??
And what is this finch
doing?!?
Perplexing Observations…
We owe much of
our understanding
of EVOLUTION to
CHARLES DARWIN.
Darwin’s Origin of Species (1859):
1. Descent with Modification (Evolution)
2. Natural Selection as a mode of Evolution
(Remember: Mendel publishes in 1866…)
Darwin’s Natural Selection:
Observation #1: Individual Variation
Darwin illustrates his mechanism with examples
from ARTIFICIAL SELECTION, the breeding of
domesticated plants and animals
Observation #2: Struggle for Existence
Inference: Differential Reproductive
Success or Natural Selection
If artificial selection can change so much in a relatively
short time, argues Darwin, then natural selection should be
capable of considerable modifications.
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Darwin also proposed that natural
selection, over time, could produce new
species from ancestral species.
This was his
explanation for
the 14 unique
species of
finches he
observed on the
Galapagos
Islands.
The Historical Context
From 1600’s +,
Geologists begin
mapping multiple
distinct layers of rock
with fossils in them.
Lines of Evidence
Naturalists begin
to study
Biogeography:
the distribution
of organisms
Many are unique
to isolated
places!
Lines of Evidence: Comparative Morphology
Lines of Evidence: Comparative Embryology
Who’s
who???
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Thus Darwin’s views are supported by
multiple, independent lines of evidence.
Evolutionary patterns of Homology that
match patterns in space (Biogeography)
and time (the Fossil Record).
Examples of
Natural
Selection?
•Insecticide-Resistant
Insects
•Antibiotic-Resistant
Bacteria
•Drug-Resistance in
HIV
ADAPTATIONS are the result of
natural selection.
Three Important Constraints on Natural
Selection:
1. Natural selection occurs only at the POPULATION
LEVEL. (Population =a group of interbreeding
individuals of the same species, sharing a
common geographic area.)
2. Natural selection can only amplify or diminish
HERITABLE VARIATION.
3. Natural selection is SITUATIONAL; an adaptation
in one situation may be useless or even
detrimental in another.
Population: localized group of individuals
belonging to the same species.
•Every species distributed over range, but
composed of multiple populations.
•Populations may be
more or less isolated.
•The total aggregate of genes in a
population at any one time is its GENE POOL
(all alleles at all loci)
MICROEVOLUTION
• Generationto-generation
change in a
population’s
frequencies of
alleles
What could
cause the
frequency of a
particular allele
to change??
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Four Primary Causes of
Microevolution:
1. Mutation
2. Natural Selection
3. Gene Flow
4. Genetic Drift
1. Mutations:
• A change in an organism’s
DNA can change the gene
pool of a population
• Important as the original source
of Genetic Variation!
• Mutations can be lethal,
neutral, or provide an
advantage!
2. Natural Selection: can affect
Types of Selection: Examples??
the frequency of traits in the
POPULATION in three different ways:
1. Directional Selection- favors one
extreme
2. Diversifying Selection- favors variants at
both opposite extremes
3. Stabilizing Selection- selects against the
extremes
3. Gene Flow:
Populations may gain
or lose alleles due to
the migration of fertile
individuals or gametes
between populations.
4. Genetic Drift:
a change in a
population’s allele frequencies due to
CHANCE.
Genetic Drift is most effective in small
populations!
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Types of Genetic Drift…
1.The Bottleneck EffectDisasters randomly reduce the
population size. The surviving
population may not be representative
of the original population’s gene pool.
Special Types of Selection:
Sexual Selection
Types of Genetic Drift…
2. The Founder Effect- a few individuals from a
larger population colonize an isolated new
habitat. Genetic drift occurring in this new
colony is known as the founder effect

Some traits are advantageous simply
because males or females prefer them
Polydactyly -- extra fingers or
sometimes toes -- is one
symptom of Ellis-van Creveld
syndrome. The syndrome is
commonly found among the
Old Order Amish of
Pennsylvania, a population that
experiences the founder effect.
Special Types of Selection:
Balanced Polymorphisms
Strange Mating Rituals…

Two or more alleles maintained in a
population by balancing selection.
Example: Sickle Cell Disease
High incidence due to
increased malarial
resistance!
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HIV and Evolution…
Malaria
and
Sickle Cell
Disease…
A colorized SEM of HIV emerging from a white blood cell.
HIV, the AIDS Virus

How HIV reproduces inside a CD4 +
T lymphocyte (T cell)
HIV is a
retrovirus.
A retrovirus is
an RNA virus
that
reproduces by
means of a
DNA molecule.
 It copies its RNA
to DNA using
reverse
transcriptase

Let’s Watch…
Integrase
Protease
HIV and Evolution…
A combination of drugs that act on different viral
targets can be used to fight HIV. This is known as
highly active antiretroviral therapy (HAART).
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HIV Evolution in a Single Patient
Following Up…
T0
T2
T1
You Try: In-Class, Part 1
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