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Nondisjunction in Animal Mitosis


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This video was made by Conly Rieder, Richard Cole, and Jennifer Waters. Drs. Rieder and Cole work at the Wadsworth Center for Cell Biology in Albany, NY, and Dr. Waters is from the University of North Carolina at Chapel Hill. This sequence appears in the video CELLebration, edited by R. Fink, published by the American Society for Cell Biology and Sinauer Associates, Inc.

Newt lung epithelial cells are extremely flat and transparent, and have large chromosomes. Small pieces of lung tissue were dissected from Taricha granulosa newts, and cultured on coverslips for 7-10 days. Mitotic cells were filmed using Nomarski differential interference optics, which give the chromosomes their nice fat 3-D look. Time compression was 1:60. The diameter of the nucleus is approximately 50 um, and individual chromosomes are on the order of 20 um long.

In this sequence, one chromosome never makes it to the equatorial plate; a condition known as nondisjunction. This occurs because the chromosome fails to form a bipolar attachment to the microtubule spindle fibers--it attaches to only one side of the spindle. When this nucleus completes dividing, the two resulting daughter nuclei will contain dissimilar chromosome numbers, and unequal amounts of DNA. An aneuploid cell may have one of several different fates. A cell with a fewer-than-normal number of chromosomes usually dies in culture. The fate of a cell an abnormally high chromosome number depends on the genes carried by the extra chromosomes. If these genes are involved in growth control, the cell may become cancerous.