In this exercise, you will look at the general shape and form of human chromosomes and observe chromosomes and the stages of mitotic division in the whitefish. You will also compare these chromosomes with the plant chromosomes studied in the previous section. Chromosome structure in animals and plants is basically the same in that both have centromeres and arms. However, plant chromosomes are generally larger than animal chromosomes.
Materials
Introduction
Cytogeneticists examining dividing cells of humans can frequently detect chromosome abnormalities that lead to severe mental retardation. To examine human chromosomes, leukocytes are isolated from a small sample of the patients blood and cultured in a medium that inhibits spindle formation during mitosis. As cells begin mitosis, chromosomes condense and become distinct but in the absence of a spindle cannot move to the poles in anaphase. You will observe a slide in which many cells have chromosomes condensed as in prometaphase or metaphase, but they are not aligned on a spindle equator.
Procedure
Materials
Introduction
The most convenient source of actively dividing cells in animals is the early embryo, where cells are large and divide rapidly with a short interphase. In blastulas (an early embryonic stage), a large percentage of cells will be dividing at any given time. By examining cross sections of whitefish blastulas, you should be able to locate many dividing cells in various stages of mitosis and cytokinesis.
Procedure
William R. Morgan wmorgan@acs.wooster.edu