Trisomy(redirected from trisome)
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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.