[Iso-X chromosomes in primary amenorrhoea and Turner's syndrome - presentation by C-banding (author's transl)].

Follow-up checks of conventionally identified iso-X chromosomes have shown dicentric X-chromosomes to be highly involved in mosaic formation (six in eight cases). The assumption is made that the high inclination of dicentric X-chromosomes to non-disjunction may cause maldistribution and, finally, result in mosaic formation. The percentual representation of certain individual lines may be drastically changed by selective gaps and by loss of dicentric X-chromosomes. The instability of dicentric X-chromosomes is a mitotic phenomenon, at the beginning of zygote formation, whereas aberration towards dicentric X or iso-X is a meiotic event.