Levan A, Levan G, Mandahl N
Cytogenet Cell Genet. 1978;20(1-6):12-23. doi: 10.1159/000130836.
For several years the SEWA mouse ascites tumor has been a carrier of double minute chromosomes (DMs), some 90% of its cells containing from one to several hundred DMs. In one specific subline of this tumor, the cells with DMs had decreased in frequency to less than 5% of the cells. At the same time, the stemline chromosome number had increased from 43 to around 50. This was due to the presence, in addition to the ordinary telocentric chromosomes, of a varying number of medium-sized metacentrics. The fact that these chromosomes deviated from ordinary mouse chromosomes in special features, such as median centromeric position, early DNA replication, and complete lack of centromeric heterochromatin, indicates that they represent a new type of chromosome. Their striking agreement with the DMs in many properties makes it tempting to associate their origin with the disappearance of the DMs.
数年来，SEWA小鼠腹水瘤一直是双微染色体（DMs）的携带者，约90%的细胞含有一到数百条双微染色体。在该肿瘤的一个特定亚系中，含有双微染色体的细胞频率已降至不到细胞总数的5%。与此同时，主干染色体数从43条增加到了约50条。这是因为除了普通的端着丝粒染色体外，还出现了数量不等的中等大小的中着丝粒染色体。这些染色体在诸如着丝粒位于中部、DNA早期复制以及完全缺乏着丝粒异染色质等特殊特征方面与普通小鼠染色体不同，这表明它们代表了一种新型染色体。它们在许多特性上与双微染色体惊人地一致，这使得人们很容易将它们的起源与双微染色体的消失联系起来。
