How Many Cats

A CIBT Lab Exercise in Molecular Biology



In this paper simulation, students will "cut" DNA samples from a mother, a baby, a husband, and a rape suspect using a restriction endonuclease. They will then "run" the DNA fragments on a "gel" to simulate the process of electrophoresis. A fluorescent probe is then washed over the gel. Finally, students will analyze the gel to identify the father of the baby.


Appropriate Levels

Biology, Honors Biology, Advanced Placement Biology.


Time Required

Teacher Preparation: Minimal. In Class: One standard class period to perform the simulation and one standard period to discuss the results.



  • large sheet of paper or poster board for gel (at least 60 cm x 80 cm) - This lab can also be done using an overhead projector and transparencies. Click on Tips for this Lab
  • scissors and tape (or glue)
  • set of base sequences representing the "Standards," "Mother DNA," "Child DNA," "Suspect DNA," and "Husband DNA"
  • set of "Probe" sequences copied onto brightly colored paper envelopes to act as wells to hold restriction fragments
Copyright for this material is held by Cornell University, the Cornell Institute for Biology Teachers (CIBT), the Center for Nanoscale Systems Institute for Physics Teachers (CIPT), and or West Hill Biological Resources, Inc., 2014. This work may be copied by the original recipient from this web site to provide copies for users working under the direct supervision of the original recipient. All other redistribution of this content without the express written permission of the copyright holder(s) is prohibited.

Price: No Charge

Ellen S. Mayo, Douglas Freeman High School, Richmond, VA

Anthony J. Bertino, Canandaigua Academy, Canandaigua, NY

Rita Calvo, Cornell University, Ithaca, NY