Chromosomes were first seen by C. Nägeli in 1842, and named in 1888 by W. Waldeyer. Walther Flemming studied and documented the behavior of chromosomes during cell division, a process he termed mitosis. We will perform experiments similar to these early scientists.
Cell division is especially rapid in the growing root tips of sprouting seeds. The chromosomes in dividing root tip cells can be demonstrated if, after we sprouting seeds or bulbs, we harvest the young root tips, and then fix, acid digest, stain, squash, and view them under a microscope.
Here is the general plan of the procedure, supplies and equipment needed:
Carnoy’s fixative (1:3 HOAc + EtOH)
Freshly sprouted seeds , about 2-3 cm long.
(rye, wheat, lentils, alfalfa, onion, etc)
Wasserman tubes (13 x 100 mm) with corks
Constant temperature “hot block”, 60 oC
razor blade and/or fine scissors
Next Day: Digest, Stain and Squash the Fixed Root Tips
12. Examine under the microscope at low power to ensure that the cells are adequately spread to a monolayer. If so, examine under higher power. Locate mitotic figures (near the tip end), and switch to oil immersion (1000x).
Here are some nice images of chromosomes from onion root tip, taken January 2005.
13. Illustrate examples of each mitotic stage (pro-, meta-, ana- and telophase). Prepare a second squash with a different species, and illustrate its mitotic stages, noting any differences observed between the two species.
Here is another page of pictures of root tip chromosomes in recent labs.
These are the four classic stages of mitosis:
14. Show chromosomes of two species of plants you have prepared to the instructor for 5 points each.