Law M L, Van Keuren M
Ann N Y Acad Sci. 1986;477:151-9. doi: 10.1111/j.1749-6632.1986.tb40330.x.
An extra copy of human chromosome 21 has been known for over twenty years to be the chromosomal abnormality in Down's syndrome; however, the biochemical and molecular basis governing expression of the phenotype is still poorly understood. Using the methods of somatic cell and molecular genetics, we have been studying genes and DNA sequences on chromosome 21 by constructing hamster/human hybrids containing a whole or partial chromosome 21 and assigning their locations on the chromosome. In particular, a family of repetitive sequences, some having only a few thousand copies in the human genome, have been used as cloned DNA markers to define deletions in these somatic cell hybrids. We have shown that this approach can significantly improve the resolution of fine chromosomal structures over the conventional cytogenetic analysis. The rationale behind this approach is the observation that a repetitive sequence probe often forms multiple bands after hybridizing to a Southern blot of digested hybrid DNA, and the band pattern appears to be unique for each human chromosome. Therefore, each band (sequence) can be assigned to a particular region of human chromosome 21 by comparing the band patterns from hybrids containing different portions of the chromosome. Results presented here showed that a 0.58-kb repetitive sequence probe can be used to identify deletions, translocations, and other more complicated rearrangements of chromosome 21 seen in patients with abnormalities of this chromosome. The advantage of using such a repetitive sequence probe over a unique sequence is that it can serve both as a repetitive sequence defining multiple sites (multiple bands on a Southern blot) in the genome and at the same time serve as a unique sequence defining a particular site (individual band). For the detection of deletions and other rearrangements, especially in small chromosomes such as 21, it is the former property that makes it very efficient in the initial assignment of a chromosome location.
二十多年来，人们已经知道多一条人类21号染色体是唐氏综合征的染色体异常情况；然而，控制该表型表达的生化和分子基础仍知之甚少。我们运用体细胞和分子遗传学方法，通过构建含有整条或部分21号染色体的仓鼠/人类杂种细胞，并确定它们在染色体上的位置，来研究21号染色体上的基因和DNA序列。特别是，一类重复序列，其中一些在人类基因组中只有几千个拷贝，已被用作克隆DNA标记来确定这些体细胞杂种细胞中的缺失情况。我们已经表明，这种方法比传统的细胞遗传学分析能显著提高精细染色体结构的分辨率。这种方法背后的基本原理是观察到重复序列探针与消化后的杂种DNA的Southern印迹杂交后通常会形成多条带，而且每条带的模式似乎对每个人类染色体都是独特的。因此，通过比较含有染色体不同部分的杂种细胞的带型，可以将每条带（序列）定位到人类21号染色体的特定区域。这里给出的结果表明，一个0.58 kb的重复序列探针可用于识别21号染色体异常患者中该染色体的缺失、易位及其他更复杂的重排情况。使用这种重复序列探针相对于单一序列的优势在于，它既可以作为定义基因组中多个位点（Southern印迹上的多条带）的重复序列，同时又可以作为定义特定位点（单个条带）的单一序列。对于缺失和其他重排的检测，特别是在像21号这样的小染色体中，正是前一种特性使其在染色体位置的初步定位中非常有效。
