Isochromosome
metacentric chromosome produced during meiosis or mitosis when the centromere splits transversely instead of longitudinally
An isochromosome is an unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other. The chromosome consists of two copies of either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a simultaneous duplication and deletion of genetic material. Consequently, there is partial trisomy of the genes present in the isochromosome and partial monosomy of the genes in the lost arm.
Nomenclature
An isochromosome can be abbreviated as i(chromosome number)(centromeric breakpoint). For example, an isochromosome of chromosome 17 containing two q arms can be identified as i(17)(q10) (seen in medulloblastoma).
Mechanism
Isochromosomes can be created during mitosis and meiosis through a misdivision of the centromere or U-type strand exchange.
Centromere misdivision
Under normal separation of sister chromatids in anaphase, the centromere will divide longitudinally, or parallel to the long axis of the chromosome. An isochromosome is created when the centromere is divided transversely, or perpendicular to the long axis of the chromosome. The division is usually not occurring in the centromere itself, but in an area surrounding the centromere, also known as a pericentric region. It is proposed that these sites of exchange contain homologous sequences between sister chromatids.
Begin with the source’s own compact description: “Isochromosome” is metacentric chromosome produced during meiosis or mitosis when the centromere splits transversely instead of longitudinally. The dossier treats that line as a proposition to test through Isochromosome, metacentric and chromosome, not as a finished interpretation.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 4, 2026. The linked authority identifier is Q900950. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Isochromosome” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.