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(cell and molecular biology)
The presence in triplicate of one of the chromosomes of the complement.



the presence of one or a few nonhomologous extra chromosomes in the chromosome set of a diploid organism. Organisms (or cells) in which one, two, or more chromosomes present themselves as three homologues are called simple trisomics, double trisomics, and so forth. Trisomy is caused by the failure of chromosomes to separate (nondisjunction) during cell division. Some specific severe disorders are the result of trisomy occurring in specific chromosomes.

References in periodicals archive ?
Trisome 9P is a rare genetic mutation in which one piece of developmental DNA - chromosomes - breaks off and joins a part of the DNA chain which it shouldn't.
Kate said: "A lot of people who have Trisome 9P start talking in their teens, I think it's about a third of them in terms of the research they've done.
It consists in a simple blood test used to identify trisome 21, known to the general public as Down's Syndrome, found in the rare fetal cells circulating in the mother's blood stream from the first weeks on pregnancy on.