Improper separation during anaphase results in a cell that has an abnormal number of chromosomes. Anaphase is part of mitosis, or the process of cell division. Anaphase is the time during which chromosomes that are lined up in the middle of a cell are pulled apart in two directions, resulting in two new cells. Errors during anaphase can result in the usual two cells after mitosis or one big cell because the two cells never split apart. In either case, the number of chromosomes is often wrong. There are different types of chromosomal abnormalities, ranging from one extra copy of one chromosome to multiple extra copies of all chromosomes.
Aneuploidy is the term that describes the situation in which a cell has a few extra chromosomes or is missing a few chromosomes. Cells with the normal number of chromosomes are called euploid. This number is different for different organisms. In humans, euploid means 46 chromosomes in each cell. For example, Down syndrome results from an extra copy of chromosome 21. Aneuploidy can happen due to what is called anaphase lag. This is when a chromosome isn’t pulled to one end fast enough during anaphase, so that when the dividing cell splits in two, one cell has an extra chromosome and the other is missing one. Aneuploidy can also result from what is called non-disjunction, which is when a chromosome fails to split in half when it is pulled in opposite directions. Non-disjunction is different than anaphase lag in that in non-disjunction, two chromosomes that should slit apart never do.
Polyploidy is the state in which a cell has a complete extra set of chromosomes. For example, human cells normally have 46 chromosomes, so a polyploid human cell could have 92 chromosomes. Since 92 is two-times more than 46, such a cell would be called diploid (“di-“ means two) because it has two sets of the normal number. However, a polyploid cell can be triploid (three sets), tetraploid (four sets), or even higher in ploidy number. If a cell is disrupted during anaphase with a drug called colchicine, which breaks the fibers that pull chromosomes apart during anaphase, polyploidy cells are often produced.
Errors in anaphase can result in cells with more than one nucleus. The nucleus is the pouch inside the cell that contains the chromosomes. After a normal mitosis in which anaphase happens normally, there are two separate cells that each have its own nucleus. Aneuploid and polyploid cells have fewer or more chromosomes than they should, but those chromosomes are housed in one nucleus in each cell. Multinucleated cells have two or more nuclei. Treating a cell with colchicine, which inhibits the fibers that pull chromosomes apart during anaphase, can result in multinucleated cells.
Asbestos is a material that was once widely used as insulation material in the walls of buildings because it helped trap heat inside those buildings. However, when disturbed, asbestos breaks into fine dust-like particles. These particles get into a person’s lungs and cause damage to cells. A animal study in the journal “Carcinogenesis” reported that cells treated with asbestos had 20 times more chromosomal abnormalities during anaphase than cells that were not treated. Treated cells had chromosomes that moved too slowly during anaphase or were two sticky to be properly pulled apart into separate cells.
- Medline Plus: Down Syndrome
- McMaster Pathophysiology Review: Aneuploidy & Non-Disjunction
- St. Ann’s College: Effect of Colchicine on Mitosis of the Onion Root Tips
- Modern Genetic Analysis: Changes in Chromosome Number
- Mutagenesis: Effect of Cytochalasin B on the Induction of Chromosome Missegregation by Colchicine at Low Concentrations in Human Lymphocytes
- Agency for Toxic Substances & Disease Registry: Asbestos Toxicity
- Carcinogenesis: Induction by Asbestos Fibers of Anaphase Abnormalities – Mechanism for Aneuploidy Induction and Possibly Carcinogenesis.
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