Download 5 Variation and Natural selection

4.1 Adaptation,Variation and
Natural Selection (p. 114-121)
Adaptation:
 
A structure,
behavior, or
physiological
process that helps
an organism survive
and reproduce in an
environment
Examples:
Needles on a
coniferous tree that
reduce water loss
  Physiological
changes associated
with hibernation
  Migration
 
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How do adaptations develop?
Adaptations arise
when a population
changes gradually
over time
  The changes in a
population are the
result of variations
within the population
 
 
A variation is a
difference
between
individuals in a
population
Some variations offer an
individual an advantage to
survival
  This means the individual
with the variation is more
likely to survive, reproduce
and pass on the variation
to its offspring
  Over time more individuals
will have this variation, and
eventually it is so common
that it becomes a
characteristic of the
population
 
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  Not
all variations are an advantage
–  Some have no effect on survival
–  Some are a disadvantage (for example a
fish born without fins)
The source of variation
  1)
Sexual Reproduction
–  In sexual reproduction offspring receive a
combination of genetic information from
both parents
–  Random combinations of this genetic
information provides genetic variation in
individuals
–  And therefore variation in the population
  2)
Mutations in genetic material
–  A mutation is a change in the DNA of an
organism
–  They occur spontaneously
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–  Some are caused by
mutagens such as UV
light or environmental
agents
–  If a mutation takes
place in a gamete
(egg or sperm) it can
be passed to offspring
A mutation can
cause a cell to
exhibit new
characteristics
  The change can be
an advantage,
disadvantage or
have no effect on
the survival of a cell
 
Example
 
A mutation in
houseflies that
makes them
resistant to DDT
–  The mutation
reduces the flies’
growth rate
–  however, it is an
advantage if the flies
are exposed to DDT
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Natural Selection
 
The process that
causes a
characteristic in a
population to
change because of
variations in
individuals
 
In natural selection the environment selects
characteristics
 
A characteristic is selected because it gives
an advantage for survival in the
environment
 
The environment exerts selective pressure
on a population
 
The population does not direct the
change: the environment selects it
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Examples of Observed Evolution
1. The excessive use of antibiotics is leading to
the evolution of antibiotic-resistant bacteria
– serious public health concern
–  Examples:
Mycobacterium
tuberculosis
–  Staphylococcus aureus
Thought Lab 4.1 p. 119
Figure 13.22
2. The evolution of insecticide resistance
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Figure 13.5B
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Sequence of events in Evolution
genetic mutation
variation in population
natural selection
(those with an advantage survive and reproduce)
speciation
Assignment
  Textbook
  page
121 questions 1-9
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