DNA Testes Lab
I originally received this lab from Steve Clark, Monterey High School, Monterey, Calif. and have used it for several years with some modifications I made. I use this lab as an introduction to DNA science to demonstrate one method of obtaining DNA from cells. This can be done with dog testes or thymus glands. It is much more memorable for the students if you use dog testes (from you local vet--Call ahead and ask him to freeze his next neuter). Keep them frozen until you use them. You can use them straight from the freezer. This lab can be done in a 40 minute span of time with excellent results. Be sure you do not use the ends of the testes. Most of the DNA is in the center.
Testes or thymus glands: frozen or fresh 2M NaCl - Cold
Crushed ice in container 95% Ethanol - Cold
2. Add 4 ml of tissue buffer (cold) and one squirt of SDS to the mortar containing the testes
3. Pick out the unhomogenized gristle and transfer the entire slurry into a test tube with stopper and add two times the volume of cold 2M NaCl. (2/3 NaCl sol. and 1/3 slurry).
4. Stopper and shake the tube for at least two minutes (your arm should get tired!). Notice the increase in viscosity. Remove the stopper. If the slurry is not in a centrifuge tube, transfer it to one now.
5. Centrifuge the tube for 7 minutes at top speed. REMEMBER TO BALANCE THE CENTRIFUGE BY RUNNING YOUR TUBE OPPOSITE SOMEBODY ELSE'S. A full centrifuge saves everyone time.
6. After centifuging, there will be two layers, a bottom precipitate or pellet of protein, and an upper liquid supernatant containing the DNA.
7. Slowly pour the aqueous upper layer (supernate) containing the DNA into a test tube and then insert your glass spooling rod.
8. Hold the test tube containing the supernate at a 45o angle and add very cold 95% ethanol (let it run gently down the sides of the test tube) to about 2 times the volume of your DNA extract.
9. Now turn your spooling rod and watch the whitish-clear DNA fibers come on to the
Explanation For Materials Or Procedures Used In Extraction
Testes or thymus gland (sweet bread) provide a high nucleus to cytoplasm ratio which
guarantees a high yield of DNA, and prevents excessive protein or lipid interference
with the procedure. Accessibility is important too. They are available from your
local veterinarian or your local butcher. Tissue must be VERY fresh, not more than
2 days old under refrigeration. It is best to keep it frozen if it is to be used
later. Grind the tissue fresh or frozen.
Sodium Dodecyl Sulfate or Sodium Lauryl Sulfate. This detergent-like substance dissolves
lipid cell membranes and denatures proteins. This will allow our DNA to come out
of the cells and into the solution.