The accurate estimation of chromatid breakage, and its relevance to a new interpretation of chromatid aberrations induced by ionizing radiations
The accurate estimation of chromatid breakage, and its relevance to a new interpretation of chromatid aberrations induced by ionizing radiations
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染色单体断裂的准确估计及其与电离辐射引起的染色单体畸变的新解释的相关性
DOI：
10.1098/rspb.1959.0043
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发表时间：
1959
期刊：
影响因子：
--
通讯作者：
S. H. Revell
中科院分区：
文献类型：
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作者：
S. H. Revell
如果细胞在接近有丝分裂时受到电离辐射，染色体就会发生变化，在中期表现为可见的染色单体结构中断，并表现为不同染色体之间的染色单体交换。这些不连续之前被解释为辐射时产生的大量染色单体断裂的残存例子，以及作为这种断裂之间新的结合的交换的结果，这些断裂发生在一起。蚕豆(Vicia Faba)的根分生组织细胞已经接受了50或65 r的X射线，用来测试对这些变化的新解释，根据这种解释，每个染色单体的不连续都是由于一条染色体上靠近的两个点之间的染色单体交换引起的。根据这一解释，中期染色单体不连续的频率应该比大多数其他像差的频率低得多：结果表明，通常获得的高值是由于包含了很大比例的短的未染色但结构上连续的“间隙”，而真正的断裂频率正如新的假设所要求的那样低。公认的是，辐射剂量和剂量强度实验表明，染色体在与单个电离粒子的轨迹相交的点上发生初级事件；而且，尽管它们本身不稳定，但在空间和时间上足够接近的这种初级事件对可以一起进入第二种稳定的交换启动状态。如果新的假说也被接受，则认为这一初级事件不太可能像通常假设的那样是染色单体断裂，也不太可能交换起始是染色单体重聚。因此，染色单体交换本身在结构上是在较晚的阶段建立的，因为两个染色体点在受影响的条件下继续联合发育。
If cells are subjected to ionizing radiations as they approach mitosis, chromosome changes are initiated which appear at metaphase as visible discontinuities of chromatid structure and as chromatid exchanges between different chromosomes. The discontinuities have previously been interpreted as surviving examples of a much larger number of chromatid breaks produced at the time of irradiation, and the exchanges as the result of new unions between such breaks that occurred close together. Root meristem cells of the broad bean (Vicia faba), which had received 50 or 65 r of X-rays, have been used to test a new interpretation of these changes, according to which each chromatid discontinuity arises from a chromatid exchange between two points close together on one chromosome. On this interpretation, the frequency of chromatid discontinuities at metaphase should be much lower than those of most other aberrations: it is shown that the high value usually obtained is due to the inclusion of a large proportion of short unstained but structurally continuous ‘gaps’, and that the frequency of true breaks is as low as the new hypothesis requires. It is accepted that radiation dosage and dose-intensity experiments indicate that chromosomes suffer primary events at the points where and when they are crossed by the tracks of single ionizing particles; and also that, although themselves unstable, pairs of such primary events that are close enough together in space and time can together enter a second stable state of exchange initiation. If the new hypothesis is also accepted it is argued to be unlikely that this primary event can be chromatid breakage, as is usually supposed, and unlikely also that exchange initiation can be chromatid reunion. It follows that the chromatid exchange itself is structurally established at some later stage, as the two chromosome points continue their joint development in the affected condition.