THE FREQUENCY AND DISTRIBUTION OF SISTER CHROMATID EXCHANGES (SCES) IN THE INDIVIDUAL CHROMOSOMES OF HUMAN KA¬RYOTYPE

The difference in the number of SCEs found per cell in 50 mitoses of control subjects when evaluated from photomicrographs or karyotypes is small but sig­nificant (p The mean value of 9.5 SCEs per mitosis found in the control group was in no way significantly different from mean values of the other groups, i.e. those consisting of pathological karyotypes and lymphoblastoid cell lines (p >0.05). High frequency of SCEs (20%) was found in the centromeric region of chro­mosomes after the 2nd and 3rd divisions in BUdR medium (6). The distribution of SCEs both observed and expected on the basis of the rela­tive length of chromosomal groups in the karyotype with results of χ2 test is shown in Table II. The changes were similar in all observed groups. The only exception were B group chromosomes of the lymphoblastoid ceil lines, where the number of breakpoints increased significantly (p We preferred to evaluate the non-banded chromosomes (G-banding considerably interferes with the accuracy of SCE calculation), the regions of break points are only roughly delineated. Even so it is clear that some regions are more often involved in SCEs than others. This is the case especially with regions 1q1, 3q2, 4q2, 8c and 16c. SCEs seem to be preferentially located on G-negative bands, as mentioned also by Morad , Jonasson and Lindsten (3)

通过显微照片或染色体核型对50次有丝分裂的对照组受试者进行分析时，每细胞中检测到的姐妹染色单体交换（Sister Chromatid Exchange, SCE）数量差异虽小但具有统计学显著性（p）。对照组中每有丝分裂平均9.5个SCE的均值，与其他各组（即携带病理性核型的组别以及淋巴母细胞系组别）的均值并无显著统计学差异（p>0.05）。在5-溴脱氧尿嘧啶核苷（Bromodeoxyuridine, BUdR）培养基中经过第2、3次分裂后，于染色体着丝粒区域检测到了20%的高频率SCE（6）。基于染色体核型中各染色体组的相对长度所计算得到的SCE预期分布与实际观测分布，结合卡方检验结果，详见表Ⅱ。所有观测组别中的变化趋势均较为相似，唯一例外的是淋巴母细胞系的B组染色体，其断裂点数量出现了显著增加（p）。本研究优先选择对非显带染色体进行分析（因为G显带会显著干扰SCE计数的准确性），且仅能对断裂点区域进行粗略界定。即便如此，仍可明确部分区域相较于其他区域更易发生SCE，尤以1q1、3q2、4q2、8c及16c区域为甚。正如Morad、Jonasson与Lindsten在文献（3）中所述，SCE似乎更偏好定位于G阴性带区域。