©David B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
University of Cincinnati Clermont College,
Batavia OH 45103
See the related protocols on Agar
Overlay Technique and Additional
Ultraviolet light induces the formation of covalently-linked pyrimidine dimers in exposed DNA. If uncorrected, these dimers can trigger changes in base sequence during subsequent replication and thus induce genetic mutations.
In human beings, these mutations are responsible for the high incidence of skin cancers among persons who spend extended periods of time unprotected in the sunlight. In bacteria, they are responsible for the germicidal effect of UV light. This latter effect will be demonstrated in this experiment, but the importance of protecting one's self from the genetic damage of UV light should apparent as well.
EQUIPMENT AND SUPPLIES:
UV transilluminater (or UV "Sunlamp"1 )
|a.||Start a stopwatch and
the plate over the edge of the rectangular UV light source to line
the 90 and the 30 regions, (exposing only the 90 second region).
for an initial 90 second. Stop watch will read 1 minuite, 30
|b.||After 90 seconds, move the
plate to the, 30/10 line, expose for 30 more seconds. (the stopwatch
will read 2.0 minutes
|c.||After 30 seconds (stopwatch says 2:00), move to the third 15/0 line, and expose for a final 15 seconds more (stopwatch will say 2 minutes 15 seconds).|
1 For UV sun tan lamps, (such as a GE 275 watt), mount the lamp 25 cm above the surface of the desk and clamp securely with a ring stand and clamp. Expose for 9, 3, 1 and 0 minutes.
2 Suggested strains:
|Initials||species of bacterium|
|EcB:||E. coli B|
|EcK||E. coli K12 lambda|