Fletcher H L
School of Biology and Biochemistry, Queens University of Belfast, United Kingdom.
Genetics. 1994 Oct;138(2):511-8. doi: 10.1093/genetics/138.2.511.
Recombination or conversion between arrays of repeated sequences need not be conservative for length because two single strands of DNA from one chromatid may form heteroduplexes in different registers on the other participating duplex. This can cause an overall change in repeat number. Loss of length conservation is equally possible whether models of recombination initiated by single-strand transfer or double-strand break are applicable. Length changing conversion will frequently produce a characteristic insertion within a deletion, often appearing as a double deletion such as are frequently found in new variants of human minisatellite MS32. There is no apparent means of preserving parity during length-changing conversion or recombination, and if the changes are biased then the overall copy number will increase or decrease according to that bias. The observation that arrays persist suggests that any bias in these arrays will be toward gains. An equilibrium may be reached where gains, which may be largely independent of array length, equal losses from the array-length-dependent processes of intrachromatid recombination and repeated unequal sister chromatid exchanges.
重复序列阵列之间的重组或转换在长度上不一定是保守的，因为来自一条染色单体的两条单链DNA可能在另一条参与的双链体上以不同的对齐方式形成异源双链体。这可能导致重复数目的总体变化。无论单链转移引发的重组模型还是双链断裂引发的重组模型是否适用，长度保守性的丧失同样是可能的。长度改变的转换常常会在缺失中产生一个特征性的插入，通常表现为双缺失，就像在人类小卫星MS32的新变体中经常发现的那样。在长度改变的转换或重组过程中，没有明显的方法来保持奇偶性，如果这些变化存在偏差，那么总体拷贝数将根据该偏差增加或减少。阵列持续存在的观察结果表明，这些阵列中的任何偏差都将倾向于增加。可能会达到一种平衡，其中增加（这可能在很大程度上与阵列长度无关）等于来自染色单体内重组和重复的不等姐妹染色单体交换的与阵列长度相关过程的损失。
