The estimation of linkage in bacteria


THE existence of genetic recombination and linkage in a strain of' Escherichia coli (Lederberg and Tatum, 1946 a, b, c; Tatum and Lederberg, 1947 ; Lederberg, i4.7) can now be regarded as definitely established. Recombination was first discovered in mixed populations. of multiple nutritional mutants by the appearance of prototrophs, which, unlike the parent types, were capable of growing in minimal media. The use of multiple mutants renders the possibility of contamination by back-mutation extremely improbable, especially as prototrophs appear only in mixed populations. The evidence suggests that the vegetative cells are haploid. The existence of linkage between some iutritional factors can be shown by testing colonies grown on a medium supplemented by a single nutritional requirement (Lederberg 1947, pp. 512-13). More conclusive evidence is provided by the introduction of other contrasting characters such as the ability or inability to ferment certain sugars, and resistance or susceptibility to various types of bacteriophage. The frequencies with which the possible combinations arise in prototrophs are most economically interpreted by postulating a linear arrangement of loci, which so far all fall into a single linkage group. In the usual type of breeding experiment the offspring can all be classified as showing no recombination or as belonging to one of a number of recombination classes. With bacteria, on the other hand, we usually examine only members of the recombination class represented by prototrophs, and even if with an improved technique we could select on the basis of factors other than nutritional factors, we should still have to classify organisms for which some recombination had been obligatory. However, it is still possible, with the aid of' certain assumptions, not only to test for the existence of linkage but also to estimate recombination fractions and to make tentative

DOI: 10.1038/hdy.1951.7

Cite this paper

@article{Bailey1951TheEO, title={The estimation of linkage in bacteria}, author={Norman T. J. Bailey}, journal={Heredity}, year={1951}, volume={5}, pages={111-124} }