| Every high school student can capture a "bit of immortality" through a laboratory experience normally reserved for higher level biology classes in college. During this chromosome lab, the students prepare, develop and stain their own chromosomes. The metaphase spread is photographed and the students then do the karyotyping of their own chromosomes (Coburn & Leygauf 1976). This lab is guarenteed to generate enthusiasm and interest. Students will get a feeling of accomplishment and excitement over the numerous, but simple steps that are required. |
A note of caution: this lab requires the withdrawal of blood from the arm by a qualified individual. Each student must have a permission slip signed by a parent or guardian.
| Students must return these signed slips before their blood can be withdrawn. Local hospitals are usually more than willing to supply the equipment and personnel for the blood withdrawal. |
The overview of the lab procedure is rather straightforward. A blood sample is taken and white blood cells grown in a special medium for three days under the influence of the mitotic stimulant, phytohemaglutinin. After 72 hours, Colcemid®, a chemical that inhibits spindle formation, is added. The red blood cells are exploded with a hypotonic solution of potassium chloride. The remaining swollen white blood cells are fixed with alcohol and acetic acid. The resulting cells are dropped from a pasteur pipette onto a clean slide, causing the cells to splatter and separate. When the slide is stained with giemsa stain, the chromosomes of the individual white blood cells are visible (Macgregor & Narley 1983).
New page showing sister chromosome exchanges.
Ordered from GIBCO/BRL, per class: GIBCO phone number is 1-800-828-6686
Needed for the class:
Glacial acetic acid (ACS grade)
Absolute methanol (ACS grade)
Incubator (capable of 37C)
Frosted glass slides
Needed for each person
Sterile 1 or 5 mL syringe
21-guage needle for the syringe
21-guage multidraw needle (for vactube)
15 mL centrifuge tube
Bulb for the pasteur pipette
70 percent isopropyl alcohol pad
A. Calibrating the centrifuge is easier than it appears. You can use a fixed sped centrifuge. Attach a voltage regular (borrowed from the physics teacher) and reduce the voltage, thus slowing down the speed of the centrifuge. You can accurately calibrate the speed using a teacher-invented Rube-Goldberg method. Place a large, sharp pencil in the centrifuge and run it on. To determine the speed, take a piece of clean white paper taped onto a firm background and hold it lightly to the spinning pencil for a one-second count. Count the marks left by the pencil on the paper. Between 9 and 15 marks will represent a rpm of 500 to 900. Adjust the voltage regulator until you obtain 9 to 15 marks.
B. Timing: the laboratory exercise takes two to three hours to finish. Students can come in on Saturday morning to do their part of the experiment. The teacher can arrange a "field trip" for half a day during the school day and have the students stay in his or her room to do the experiment. A substitute teacher can take the regularly scheduled classes to the library for research, study or a written assignment. This procedure may be used for a small number of select student(s) rather than an entire class.
C. Slides are observed under high power (400 X) and then photographed under oil immersion. Students may spend a few days determining the best metaphase spread. Each time a student feels that he or she has found a good spread, the teacher marks their slide close to the spot with a fine-tip black lab marker. When the students are all done, they tell the teacher which dot they want to have photographed. The local hospital's cytology department will often allow the teacher to use the scope and camera (with supervision). It is very helpful when it come to photographing slides. The slides are photographed under oil immersion with black and white film. Make friends with the local hospitals department staff. Explain your goals and ask them for help.
D. Cost: the cost of this experiment is relative to what you may have on hand. A general figure of $30 to $70 per 10 students is a good guess. The cost incurred to an individual by a hospital runs many hundreds of dollars, almost $1,000.
Coburn, S.P. & Leyauf, R.B. (1976).
Human chromosome analysis biokit. Burlington,
NC: Carolina Biological Supply Co.
Kaplan, B.J. (1978) Preparation of the normal
karyotype (workbook). Chicago: American
Society of Clinical Pathologists.
Macgregor, H.C. & Narley, J.M. (1983).
Working with animal chromosome. New
York: John Wiley & Sons
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