Wann M, Mahajan S K, Wood T H
J Bacteriol. 1970 Sep;103(3):601-6. doi: 10.1128/jb.103.3.601-606.1970.
Conventional methods for chromosomal mapping in Escherichia coli are (i) interruption of matings to obtain minimum marker entry times, (ii) linkage analysis of recombinants, and (iii) cotransduction. Method (i) has a resolution of about 0.5 min (5 x 10(4) nucleotides) and is not useful for distances less than about 1 min; methods (ii) and (iii) are capable of better resolution but are generally not very reproducible and no general theory is available for translating crossing-over and cotransduction frequencies into physical chromosomal distances. We found that when merozygotes are irradiated (X rays or ultraviolet light) soon after marker transfer, high linkage values (0.8 to 1.0) between nearby marker pairs decrease with radiation dose to 0.5. Our results are quantitatively consistent with the idea that radiations induce crossing-over lesions proportional to dose, and the number of such lesions between two markers is proportional to the physical separation of the markers in the range that can also be measured by interruption of mating (0.5 to 4.0 min). Additivity relations among markers are also satisfied. We used this technique to measure the distances (0.1 to 1.0 min) between several pairs of closely linked markers.
（i）中断交配以获得最小标记进入时间；（ii）对重组体进行连锁分析；（iii）共转导。方法（i）的分辨率约为0.5分钟（5×10⁴个核苷酸），对于小于约1分钟的距离无用；方法（ii）和（iii）能够实现更高的分辨率，但通常不太可重复，并且没有通用理论可用于将交换频率和共转导频率转化为染色体的物理距离。我们发现，当部分二倍体在标记转移后不久受到照射（X射线或紫外线）时，相邻标记对之间的高连锁值（0.8至1.0）会随着辐射剂量降低至0.5。我们的结果在定量上与以下观点一致：辐射诱导的交换损伤与剂量成正比，并且两个标记之间这种损伤的数量与标记在通过中断交配也能测量的范围内（0.5至4.0分钟）的物理间隔成正比。标记之间的加性关系也得到满足。我们使用这种技术测量了几对紧密连锁标记之间的距离（0.1至1.0分钟）。
