A CLASSROOM DEMONSTRATION OF GENETIC REARRANGEMENT

This simple demonstration of genetic rearrangement may be modified to suit the needs or format of your class.

Time requirements:
Preparation time may vary depending upon the number of student assistants.
This demonstration usually requires 20-25 minutes to complete.
Explanation and review of the demonstrated results usually requires 15-20 min. Materials:
1 roll of adding machine paper
several marker pens
scissors
clear tape

Begin by preparing the roll of paper. (This task may be done by the instructor, or may be performed by any number of student assistants.) It is a good idea to cut the paper into five or six foot lengths before you write the sentences upon each strip. Using a marker pen, write on one side of the long thin adding machine paper any common text. The choice of text is optional. A selection from some well known text, such as the Declaration of Independence or the first page of a popular novel, is suggested. Thus you will produce several long strips of paper, written upon each will be a complete sentence. This will assure a supply of strips of approximately uniform lengths. Spaces may be left at the beginning or end of the strips, so that the sentences fill each strip. Since the starting material for this demonstration is many long strips of paper with complete sentences, you should not choose text that deviates from this syntax (do not use poetry or free verse.) You should produce enough strips of paper so that each student in the class will have at least one strip. (Make a few extra strips, just in case some of the original strips are accidentally ripped while the demonstration begins.)

Students should work in groups of three. Two students will each hold a sentence strip (that's two strips) and the third student will function as an enzyme. The two students with the two strips may consider themselves to be chromosomes. The student functioning as an enzyme will be responsible for the action of the scissors and the clear tape. A review of the function of enzymes will remind students that enzymes aid in the separation of base pairs as well as other enzymes aiding in the repair or fusing of base pairs.

The 'chromosome' students will take their paper strips (that's one strip each or a total of two strips for each pair of students) and place them 'back-to-back' (The blank side of the strip against the blank side of the other strip.) If one student holds the left end of these two strips and the other student holds the right end of these two strips, we have two long strips of paper with sentences written on the outward facing sides. Now the chromosome students should 'twist' the strips a few times to introduce some twists into the joined pairs of paper. The number of twists is optional. However, each pair of students should not choose the same number of twists. So the instructor may wish to suggest that the first pair twist their strips once, the second pair twist their strips twice, and so on until there are many differing amounts of twists in all the pairs of strips throughout the classroom.

The paper chromosomes are now ready to undergo enzyme lysis. The student 'enzymes' will examine each strip and with the scissors cut each strip BETWEEN any pair of words. Please remind the enzyme students to cut between words, so that they don't sever any word in two. To do this the enzyme students must examine the words on the paper strips and cut each strip separately. Do not cut both strips with one cut. Each strip should be cut separately at some point close to the other strip. In other words if the enzyme student decides to cut the first strip very close to the left side the second strip should also be cut in this region. This process of cutting or lysis will separate the strips leaving each chromosome student with two shorter strips of paper.

Putting away the scissors, the enzyme will now function to repair the strips of chromosomes. However, they must perform this task without looking at the words written on the strips. The chromosome students should separate the two strips that each holds into left and right hand. (The original twisting should provide a random mixing of these strips.) The enzyme student now takes the loose end of the left hand strip from one chromosome student and joins in to the loose end of the left hand strip from the other chromosome student and without looking at the word (holding the strip with the word-side down) tapes the two strips together.

Note: a variation on this basic theme may include extra students to take up the loose ends of any remaining long chromosomes and permit the enzymes to cut these in the same fashion, thus forming three separate strips for each original chromosome. The taping process for this requires that three shorter strips of paper will be taped to re-form the original chromosome.

At this point each strip of paper, representing a chromosome, has undergone genetic re-arrangement.

Examining the strips of words will tell us something about this process. Some strips will contain the original sentences. These were cut and reformed as they originally were. Others will contain fragments of sentences and will not be grammatically correct. These may be used to represent lethal mutations or re-arrangements. Still others will contain joined sentence fragments that are grammatically correct and yet different from the original sentences. These may be nonsense sentences but if they have proper syntax they will survive. These will represent new arrangements in chromosomal material. These also represent the essence of the idea of chromosomal shift. Genetic material shifting from its original positions to new and viable positions.

DISCUSSION:

Older theories (Darwinian) stated that changes in the environment and random mutations favored or hindered certain physical characteristics. Thus, environmental changes help drive evolution. Ecogenetic theories take a bolder stance and say that mutations (in many forms) drive organisms (plants and animals) to specific local environments that they seem more adapted to be within. Both theories seem to explain evolution.

Ordinary enzymatic processes contribute to the re-arrangement of genetic material within a given chromosome. The movement of genetic material is termed 'genetic shift.' Sometimes the movement of genes or parts of genes within a chromosome may lead to mutations within the phenotype of an organism. The survival and reproduction of that organism contributes to the survival of this 'shifted' gene.

Of course, for this demonstration we used sentence structure as an analogy for genetic structure. Many random combinations of genetic base pairs are nonsense in just the same why many combinations of random words produce nonsense sentences. Only those combinations that code for the production of 'real' compounds may produce viable organisms. Many combinations of genetic material code for real substances yet these substances may be lethal to the organism. Such genes will kill the organism and not be passed on to any offspring.