DNA PROFILING SIMULATION - Where’s the CAT?
Background - DNA profiling involves the use of gel electrophoresis to separate fragments of DNA according to their size. These fragments have been generated by treating DNA with restriction enzymes - enzymes that cut DNA at specific sites. The electrophoresis works on the principle that a charged molecule will migrate towards the pole of the opposite charge, and that smaller particles will migrate faster because they make fewer collisions with the molecules in the agarose gel. This technology is applied to criminology by comparing DNA recovered from a crime scene with a suspects DNA. It is also applied to paternity situations by comparing DNA from a child to prospective fathers. This technology is also applied to compare the degree of relationship of two organisms, both interspecific and intraspecific. (refer to your notes for detail on the steps.)
Purpose - This activity simulates the action of a DNA profile. By completing this you will understand the principles of DNA profiling.
Procedures - each group should pick up the following:
1 sheet of standard/ mother DNA
1 sheet of husband/suspect/ child DNA
1 strip of colorful probes
1. Be sure to keep each individuals DNA separate from the others. Cut each DNA sample into strips. Tape the strips of each type (standard with standard; mother with mother….) together, obscuring the subscripts – COVERING THE NUMBERS, so that you have one long strip of DNA for each individual/standard.
2. Cut the colorful probes into three base segments reading “GTA”
3. Scan your DNA strip until you find “GGCC.” Cut across the strip between the center G and C - much like a restriction enzyme would. This should form a fragment that ends in GG and another that begins with CC. Each sample should have five of these sites, so each sample should yield six fragments. The standard contains seven such sites yielding eight fragments.
4. Count the number of bases on each fragment and write that number on the front of each fragment.
5. Using the large lab tables, set up five different columns for each DNA sample - standard, mother, husband, suspect, child. Label each column to avoid confusion.
6. Simulate electrophoresis by separating the fragments according to size. First separate the standard. Remember that the larger fragments migrate slowly and the smaller ones migrate further.
7. Check with me at this point before proceeding further.
8. Attach the probes to the appropriate sites.
9. Determine the identity of the child’s father.
10. Check with me for understanding.
11. Answer the attached Post-activity Questionnaire.