. Cell heredity. Cytogenetics. 148 CELL HEREDITY S a b T. FIGURE Diagrammatic representation of two hypotheses of prophage recombi- nation. In the upper diagram the prophage (white line) is shown completely inserted in the bacterial chromosome (black line). In the lower diagram only a short segment is inserted. In the former case, but not in the latter, an exchange between b and c would recombine the outside markers S and T (after Jacob and Wollman, 1959, in: Tunewoll, Recent Progress in Microbiology, p. 15, Springfield, III., Charles C. Thomas). prophage in lysogenic cells. Whether this
. Cell heredity. Cytogenetics. 148 CELL HEREDITY S a b T. FIGURE Diagrammatic representation of two hypotheses of prophage recombi- nation. In the upper diagram the prophage (white line) is shown completely inserted in the bacterial chromosome (black line). In the lower diagram only a short segment is inserted. In the former case, but not in the latter, an exchange between b and c would recombine the outside markers S and T (after Jacob and Wollman, 1959, in: Tunewoll, Recent Progress in Microbiology, p. 15, Springfield, III., Charles C. Thomas). prophage in lysogenic cells. Whether this is true of all reducible epi- somes is yet to be seen. Only one prophage has been found in E. coli which does not segregate in crosses as would be expected if it were located on the chromosome. is inherited maternally, always from the F~, it seems to have an extrachromosomal residence. It is interesting that this prophage yields the only type of phages that will nonspecifically transduce many different genes in strain K12. Although most work on bacterial mating has been done with one strain of E. coli, K12, many other strains have been shown to undergo the process. It has even been possible to cross E. coli with Shigella dysenteriae and with Salmonella typhimurium, raising questions about the meaning of genus and species in such organisms. Furthermore, other bacteria, such as Pseudomonas and Bacillus, have been shown to mate, and so have the commercially important bacterialike organisms, Strepto- myces. In the last two cases, however, all strains do not show a pattern of recombinant types among the offspring that allows an interpretation of gene exchange in terms of crossing over or copy-choice mechanisms in a linkage group with genes in a linear order. Indeed, out of such matings come new genotypes that do not reflect the parental genes which entered the cross. Whether such phenomena are to be explained on the. Please note that these images are extracted from scanned
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