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An abnormal (tripolar) mitosis (12 o'clock position) in a precancerous lesion of the stomach. H&E stain
Although errors in mitosis are rare, the process may go wrong, especially during early cellular divisions in the zygote.
Mitotic errors can be especially dangerous to the organism because
future offspring from this parent cell will carry the same disorder.
In nondisjunction, a chromosome may fail to separate during anaphase. One daughter cell
will receive both sister chromosomes and the other will receive none.
This results in the former cell having three chromosomes containing the
same genes (two sisters and a homologue), a condition known as trisomy,
and the latter cell having only one chromosome (the homologous
chromosome), a condition known as monosomy.
These cells are considered aneuploid, a condition often associated with
cancer. Occasionally when cells experience nondisjunction, they fail to
complete cell division and retain both nuclei in one cell, resulting in
binucleated cells.[citation needed]
Mitosis
is a demanding process for the cell, which goes through dramatic
changes in ultrastructure, its organelles disintegrate and reform in a
matter of hours, and chromosomes are jostled constantly by probing microtubules.
Occasionally, chromosomes may become damaged. An arm of the chromosome
may be broken and the fragment lost, causing deletion. The fragment may
incorrectly reattach to another, non-homologous chromosome, causing
translocation. It may reattach to the original chromosome, but in
reverse orientation, causing inversion. Or, it may be treated
erroneously as a c,
causing chromosomal duplication. The effect of these genetic
abnormalities depends on the specific nature of the error.[citation
needed]
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