Who, What, Where, When and Why?
Science (scientia : to know)
The Scientific Method: A model for
problem solving that follows a well
defined procedure
Defining the Problem
What is causing limb mutations in Amphibians?
Collecting Information
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Amphibian skin is permeable to substances in
the water, air and land.
Amphibians start their life in water and end up
land; they are exposed to many threats
Increased UV radiation is getting through a
thinning ozone layer.
Retinoic acid occurs in vertebrate embryos and
influences the development of limbs.
Trematode cysts have been found clustered in
developing limb buds.
Hypotheses
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Increased UV radiation is damaging the genes
directing limb development (R. Mc Kinnell)
 Chemicals in the water, acting either singly or
together, are penetrating the frog’s skin
causing mutations.
 Abnormally high concentrations of retinoic
acid and similar chemicals are affecting limb
development at the tadpole stage. (J. Bantle)
 Trematode cysts are splitting developing limb
buds in multiple places. (S. Sessions)
Testing the Hypotheses
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Tissue samples are observed under the microscope.
Searching for damaged chromosomes. (Mc Kinnell)
 Tadpoles are incubated for 72 hours in a solution
containing an insecticide that was subjected to UV
radiation. (Previous tests indicate that certain
insecticides are transformed into retinoid like
compounds in the presence of UV radiation.
J. Bantle)
 Plastic beads are surgically implanted into
developing limb buds. The beads mimic trematode
cysts. The tadpoles are allowed to develop under
normal conditions. (S. Sessions)
Conclusions
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No visible genetic damage was determined with
the technique used by Mc Kinnell. Other
techniques will be applied to retest the hypothesis.
 Bantle concluded that insecticides can be
transformed into chemicals (when subjected to UV
radiation) that can cause mutations like those
observed.
 Sessions showed that plastic beads inserted into
developing limb buds can cause mirror image
duplications. Actual cysts need to be implanted
into developing limb buds and analyzed.