1. Mice should be weaned (at least 3 wk old) before they are biopsied.
2. At the same time as the tail tissue is obtained, the mouse should be tagged in one of four ways:
a. Ear punching;
b. Toe clipping (a toe clipping scheme is shown in Fig. 1);
c. Caging (weaned animals can be placed individually in marked cages);
d. Electronic tagging systems are now available (Lab Products Inc., May wood, NJ).
3. If the DNA is to be used for polymerase chain reaction analysis (see Chapter 36), cross-contamination, which can be introduced by the scissors, should be avoided. The tail tissue will digest without mincing.
4. Approximately 100-200 mg of genomic DNA can be isolated from 1 cm of tail tissue, which is sufficient for a large number of Southern analyses. The quality of the DNA is such that it is cleaved by most common restriction endonucleases.
5. Vortexing and repeated freeze-thawing sheers genomic DNA and should be avoided.
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