Linear Inheritance in Transductional Clones.

mutation or segregation may intervene, but further descendants will again follow this rule of clonal heredity, which is the corollary of equal division. But other rules of inheritance are known-for example, the entailment of estates in land and the traditional law of primogeniture in titles of nobility-whereby a legacy must pass undivided through a single line of descent through the generations. This paper will have to do with biological analogies of linear inheritance which have appeared in experiments on the transduction of motility-genes in Salmonella. Transduction is a mechanism of genetic recombination which is notable for the transfer of hereditary fragments from one cell to another (SYMPOSIUM 1955, LEDERBERG 1956a). In these experiments, a temperate bacteriophage serves as vector for the fragments, which are furnished by the disruption of the chromosomes of a bacterial host as it supports the growth of the phage. When this crop of phage is applied to cells of a suitably marked recipient strain, some (1W6) of these cells yield a transformed clone which carries a given marker from the donor. In previous studies, the transformed clones have exhibited the same genotypic stability as did the parents. However, the selective methods which were used to isolate the rare recombinants would overlook transductional effects that did not yield substantial clones of the new types. These studies included auxotrophic, fermentative, resistance, serological and motility markers, and each one for which a suitable selective technique was available was subject to transduction in much the same fashion. The following experiments are a follow-up of observations on “motility trails” (see paragraph 1. 1) initiated by DR. BRUCE STOCKER during a research visit to this laboratory (STOCKER, ZINDER and LEDERBERG 1953). After his return to England, DR. STOCKER began microscopic studies on these trails; the immediate concern here was the problem of segregation and crossing over in transductional clones. However, the two studies proved to be operationally inseparable. I am indebted to DR. STOCKER for an unreserved exchange of materials, information and manuscript drafts throughout these studies. In the main, the terminology also follows his suggestions. A concordance of my results and interpretations with his (STOCKER 1956b) is given a t the close of this paper. Glossary and symbols. The central concept of this paper is that of a line (adj. linear or unilinear) which signifies a single, unbranched, finite or infinite chain of descent