SCANNING ELECTRON-MICROSCOPY OF FRAGMENTARY MARKER CHROMOSOMES OBSERVED BY LIGHT-MICROSCOPY

To study the fine structure of fragmentary marker chromosomes, we perf ormed scanning electron microscopy (SEM) on samples isolated from two carriers (Case 1: 46, XP/47, XP, +mar/48, XP, +mar, +mar; Case 2: 47, XY, +mar). In both cases, light microscopic observation revealed that marker chromosomes lacked a centromere and were fragmented in appearan ce. However, SEM observation of the metaphasic cells in both Gases sho wed three variations. One variation was a structure that seemed to be metacentric, another was a structure that seemed to be submetacentric, and the remaining one was essentially fragmentary. However, neither t he usual chromatid nor centromere formations were observed in the meta centric-like and submetacentric-like structures, even when both cases were observed by SEM. Moreover, the marker chromosomes of the boy of C ase 1, who suffered from various clinical troubles, included a greater population of metacentric-like or submetacentric-like structures than of essentially fragmentary structures. The marker chromosomes of the fetus of Case 2, who suffered from no clinical problems, included a mu ch greater population of essentially fragmentary structures than metac entric-like or submetacentric like structures. Therefore, SEM observat ion of fragmentary marker chromosomes that are visible on light micros copy might be used to define specific structures. Moreover, SEM observ ation might provide clinical criteria relating to the pathogenesis of fragmentary marker chromosomes found on light microscopy.