Note: This activity and extension ideas are from Scientific American Frontiers Online (AOL keyword: sci am)
Close, Closer, Closest
An animal's genetic makeup can be analyzed using a technique called restriction mapping. In this process, strands of genetic material are first attacked by enzymes that cleave the DNA at specific sites. Next, the fragments resulting from this cleavage are sorted in a chromatography-like process called electrophoresis. If samples from two organisms contain a similar assortment of DNA fragments, then the organisms are closely related. If fragment concentrations are dissimilar, the organisms are less related. In this activity, you will perform an experiment that models this type of DNA analysis.
- Mock DNA solutions-two or more food coloring dyes diluted with water
- coffee filters or paper towels
- container for water
- paper clips
- Cut coffee filters into five strips, each about 1cm wide and 10cm long.
- Using a toothpick, transfer a drop of one DNA mock solution to one of the strips. Place the drop in the middle of the paper strip, about 2cm above the lower edge. Let the solution dry.
- Repeat Step 2, using a different strip of filter paper for each of the mock DNA solutions.
- Place a paper clip on the upper edge of each strip. Then, slide a straw through the clips. The strips should hang freely.
- Pour about 1cm of water into the container.
- Position the straw over the container so that the strips contact the water (the dots should be about 1cm above the surface of the water).
- After 15 minutes, examine the strips. Compare your strips with other samples in your own collection and with samples of other students.
This activity can be performed by individuals or in groups. Make five mock DNA solutions using food coloring; three should be similar and two dissimilar. Each group or individual should have one sample of each of the five solutions.
- What happens to the sample drops?
- Which samples have a similar makeup?
- Which samples appear dissimilar?
- How can you apply your observations to restriction mapping?
1. They separate into colors as they travel up the paper.
2 and 3. Answers will vary.
4. Like solutions of DNA fragments, the food-coloring solutions separate into components. Similarities and differences in the components are then used to classify the solutions. Solutions that show similarities are analogous to restriction mapping of closely related species; dissimilar solutions represent distant relations.
Introduction by Richard Lord
Biology doesn't lend itself to spectacular demonstrations as well as chemistry and physics do. However, a demonstration is a great way to get or keep attention and it does add spice to a classroom presentation. Many good demonstrations can be adapted from experiments in various lab manuals. And some demonstrations can also be expanded to lab investigations. Often a demonstration will be remembered long after a description has been forgotten. With that in mind, I present a set of simple and effective, though perhaps not spectacular (nothing explodes), demonstrations that can be used in the classroom. Some of the demonstrations involve use of hazardous materials. Appropriate safety precautions should always be taken.
I am still collecting good demonstrations and would be delighted to hear from anyone who has any that they would be willing to share. Send them to me an America Online (RNLORD) or regular mail to Richard Lord, Presque Isle High School, 16 Fort Street, Presque Isle, ME 04769. Someday, I hope to compile them all into a book (along with a great deal of other material I have collected).
Gene Splicing: Contstruction paper
To show a simple illustration of how gene splicing is done.
Materials: Construction paper, glue, scissors, stapler with staples
Procedure: Before class, cut a long thin strip of construction paper and glue or staple it into a loop. When discussing the procedure of gene splicing, cut the loop (plasmid) with the scissors
(restriction enzyme). Then with glue or stapler (ligase), attach another strip of construction paper (inserted gene) into the loop.
Gene Splicing; Film
To demonstrate by analogy the process of gene splicing
Materials: Several lengths of 16mm film, scissors, tape
Procedure: Take a long piece of film which you have previously taped into a loop. Now take another length of film and cut a "scene" from it. Cut open the loop and, using tape, splice the new scene into it. Make the analogy that films and tapes are made by splicing scenes together just as a gene sequence (new scene) is spliced into an existing plasmid or chromosome (original loop), using restriction enzymes (scissors) and ligases (tape).