Transcript Adaptation and Evolution

The Challenges of Making a
Living
Learning Objectives
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Review the levels of organization in living things, the importance of
homeostasis, & how this stable internal environment (within the
“zone of tolerance”) is maintained.
Differentiate between short-term and long-term adaptations. Explain
the genetic component of homeostatic mechanisms as well as longterm adaptations to the environment.
Describe the similarities and differences among behavioral, cellular,
and genetic adaptations, including examples of each.
Describe the potential mechanisms of genetic adaptation, and
explain how these genes & the natural environment interact.
Explain Charles Darwin’s 4 postulates regarding the origin of
species, in the context of his observations about populations.
Describe several examples that provide additional evidence that
populations evolve, potentially producing new species, by the
process of natural selection. How are the results of natural selection
different from the other processes of evolution?
Compare and contrast the evolutionary processes known as genetic
drift and gene flow.
Compare and contrast stabilizing selection, directional selection, and
disruptive selection.
p. 404
Structural Organization
• Most plants and animals have
cells, tissues, organs, and
organ systems
• A plant or animal body becomes
structurally organized during
growth and development
– Growth: cells increase in number,
size, volume
– Development: specialized tissues,
organs, and organ systems form
• Animals have “control centers” to
regulate body function in the
short-term, whereas plants have
decentralized control over function
What are some of the challenges associated with large body size?
If all somatic cells in an organism have the same genetic information,
how can cells specialize into tissues & organs?
Homeostasis
= the maintenance of a dynamic
equilibrium
• Plant and animal cells must be
bathed in a relatively stable fluid
that delivers nutrients and carries
away metabolic wastes in order
to stay alive
– Why might an organism’s
internal environment change?
– Why is a stable internal
environment important to an
organism’s survival? Describe
an example.
p.
p. 405
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Maintaining Homeostasis
What are the common challenges?
• O2 & CO2 gas exchange
• water-solute balance
• signaling molecules to
guide events on the
cellular level
• live within specific
habitats, and respond to
environmental threats
p. 406
• Behavioral adaptations
– e.g. thermoregulation
• Cellular adaptations
– e.g. aclimatization
– intercellular communication
• Genetic adaptations
– new allele combinations
– mutations
Describe an example of a mechanism to adapt to short term changes
in the environment. Is your example a behavioral or cellular
adaptation? Where does it occur, and how long does it last?
Describe the scope of a genetic adaptation in terms of the number of
individuals affected, and the time period over which it occurs.
Zone of Tolerance
Stable operating conditions in the internal environment (in the blood and
tissue fluid) is maintained by the coordinated activities of cells, tissues,
organs, and organ systems
High
# individuals
Optimum range
Stress
Stress
Intolerance
Intolerance
homeostasis
Low
Internal Condition
High
Behavioral Adaptations
Cellular Adaptations
Genetic Adaptations
How do genetically derived adaptive traits within
a population come about?
– Crossing Over
– Independent assortment
– Fertilization
– New alleles (gene mutations)
Describe how a genome might be
changed by these 4 mechanisms.
How might the gene pool be altered
when these sources of variation arise?
p. 246
Gene Pool
What is a gene pool?
What is the
relationship between a
gene pool and a
popluation?
What might cause
changes in the gene
pool?
Is this evolution?
http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_GenePool.html
Gene Mutation
• Change in the structure of DNA in
gametes.
p. 248
Amino acid redundancy allows
for fewer mutations
Figure
similar to
one on
p. 198
Gene Mutation
p. 248
• Rare!
– 1 gamete in 100,0001,000,000
• Neutral (why?)
• Deleterious
– Changes the shape of
a protein
– Stops synthesis of a
protein too early
• Advantageous
What will likely happen to deleterious mutations in a population?
Charles Darwin’s radical idea
(…or was it?)
p. 242
• Meticulous observation
• Considered numerous
possible relationships,
especially b/w animals
and their environment
• 2 main points:
– Species evolved from
ancestral species
– Natural selection was
the mechanism for this
evolutionary change
What is a species?
On the Origin of Species
• Descent with modification
(aka evolution) is the
explanation for life’s unity
and diversity
– all organisms are related
via a common ancestor
– adaptations developed as
descendents from a
common ancestor moved
into new habitats (or the
habitat changed)
Darwin’s metaphor for the history of life was a branching tree.
Observation 1
• Species have a
great potential for
reproduction
• Populations would
increase
exponentially if all
individuals survived
and reproduced
p. 243
Observation 2
• Populations
tend to remain
stable over
time, except for
mild seasonal
fluctuations
and occasional
severe
fluctuations
Moose population on island in Lake Superior
p. 243
Observation 3
• Natural resources are limited, i.e. there is a
struggle for existence
p. 243
Observation 4
• No two individuals are exactly
the same; rather, every
population displays enormous
variability.
p. 243
Observation 5
• Much of this variation
is heritable
• However, Darwin did
not know the
mechanism of
inheritance
p. 243
Darwin’s 4 postulates
1. Individuals within species are variable.
2. Some of these variations are passed onto offspring.
3. In every generation, more offspring are produced
than can survive.
4. Survival and reproduction are not random.
The individuals that survive and go on to
reproduce, are the ones with the most favorable
variations.
p. 243
Other Evidence for Evolution
• Organisms are
adapted to
their
environments
• Camouflage is
an example of
evolutionary
adaptation
A floral mantid (insect pollinator)
Other evidence
• Examples of “natural”
selection over short
periods of time
Is it fair to describe
this as natural
selection?
How is this similar to
antibiotic resistance
among pathogenic
bacteria?
Evolution of resistance to insecticides
in insect populations
Other evidence
• Selective breeding & artificial selection
Vegetables developed by humans from wild mustard plant
through selective breeding
Other evidence
• Homologous structures
Forearm bones in mammals
Other evidence
Ribosomal structure (large subunit of
bacterial ribosome)
• Molecular “record” –
molecular
homologies
Other evidence
• Fossil record
Fossil Trilobites
Elephant evolution based on fossils
Alterations to the Gene Pool:
Gene flow
• As individuals or gametes flow between
populations, they become more similar. The
reverse is also true.
p. 255
Alterations to the Gene Pool:
Genetic Drift
• With low population
size, alleles (i.e.
traits) can
disappear
How might this happen?
Has evolution occurred?
Is the population more fit?
p. 254
Alterations to the Gene Pool:
Directional Selection
Deaths due to
pesticides
decreased over
time.
What determines
which alleles are
selected?
p. 249
Alterations to the Gene Pool:
Stabilizing Selection
p. 250
Previously,
those babies
that were too
small did not
survive and
those that were
too big had
complications.
Does this imply
that birth weight
is an inherited
trait?
Alterations to the Gene Pool:
Disruptive Selection
Large billed
individuals crack
hard seeds.
Small billed
individuals crack
soft seeds.
Intermediate forms
do not crack either
seeds well.
p. 251