Ved Brat S, Verma R S, Dosik H
Hum Genet. 1981;56(3):305-8. doi: 10.1007/BF00274684.
Isolabeling observed during sister chromatid differentiation (SCD) was studied from human skin fibroblasts by the fluorescence-plus-Giemsa (FPG) technique. Bromodeoxyuridine (BrdU) was fed to exponentially dividing cells for 52 h to enable completion of two consecutive cycles of DNA replication. During this period, the late-replicating regions of some chromosomes were able to go through three replication cycles. These chromosome regions had evidently incorporated BrdU bifiliarly in both chromatids and hence, on staining with FPG, appeared isostained (isolabeled). Thus, incubation of exponentially dividing cells with BrdU for a period longer than that required for two cell cycles appears to be a suitable method for revealing the late-replicating regions of the genome, such as the X chromosome in a human female, as isolabeled. In another experiment with Indian muntjac chromosomes, isolabeled segments were darkly stained, which suggested unifilar incorporation of BrdU. In this case, unequal crossing-over or an unequal distribution of thymine residues probably is responsible for the isolabel.
通过荧光加吉姆萨（FPG）技术，在人类皮肤成纤维细胞中研究了姐妹染色单体分化（SCD）过程中观察到的等标记现象。将溴脱氧尿苷（BrdU）添加到指数生长的细胞中培养52小时，以使DNA复制能够完成两个连续的周期。在此期间，一些染色体的晚复制区域能够经历三个复制周期。这些染色体区域显然在两条染色单体中都双股掺入了BrdU，因此，在用FPG染色时，呈现出等染色（等标记）。因此，将指数生长的细胞与BrdU一起孵育一段比两个细胞周期所需时间更长的时间，似乎是一种揭示基因组晚复制区域（如人类女性的X染色体）为等标记的合适方法。在另一项针对印度麂染色体的实验中，等标记的片段被深染，这表明BrdU是单股掺入的。在这种情况下，不等交换或胸腺嘧啶残基的不均等分布可能是造成等标记的原因。
