Cytological evidence of defective template in the fragile X chromosome

B. Kerem, R. Goitein, T. Schaap*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


In cells of fragile X patients, the changed X segment may appear as a poorly staining region or a gap, or as a deletion, involving one or both chromatids. To find out whether the fragile site represents ah incompletely replicated DNA sequence, as has been suggested recently, we analyzed the four chromatids of methotrexate-induced endoreduplicated fragile X chromosomes. Our main observations were: (1) a deleted chromatid was never internal to a poorly staining one; (2) an endoreduplicated X chromosome with a fragile site never included a normal chromatid. These results can be explained by assuming that DNA at the fragile site, when replicated in the presence of methotrexate, may undergo defective replication and give rise to improperly packaged chromatin, appearing as a chromatid with a poorly staining region or a gap in the following metaphase. The same DNA may fail to function as a template in the following S-phase and give rise to a chromatid with a single-stranded segment, appearing as a deleted chromatid in the following metaphase.

Original languageAmerican English
Pages (from-to)6-10
Number of pages5
Issue number1
StatePublished - Sep 1988
Externally publishedYes


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