MOLECULAR CHARACTERIZATION OF ISOCHROMOSOMES OF XQ

We have undertaken a study of 35 patients with i(Xq) to determine whet her those that are maternally derived originate by similar mechanisms to those that are paternally derived. Isochromosome formation is not a ssociated, with increased parental age and > 90% of i(Xq) contain prox imal Xp sequences suggesting that cen centromere misdivision is not a common mechanism of formation. Our results indicate that the majority of i(Xq) originate from a single X chromosome and the usual mechanisms of formation do not appear to differ according to the parent of origi n.