Genetics 



The distribution of non-selected markers among the recombinants is also 

 affected by the nature of the crosses. In a cross of Hfr ly~ Lac^ Gal+ X 

 F~ ly~ Lac~ Gal~ 55% of the recombinants are Lac"^, 45% are Gal"*". 

 The simultaneous passage of lac+ and Gal+ occurs in 40% of the cases, 

 which indicates linkage between Lacj and GaU. In a cross of Hfr ly"*" 

 Lac+ Gal| X F~ ly~ Lac^ Gal~, in contrast, 25% of the recombinants 

 are Lac,+ but only 3% are Gal"*", of which about half are also Lac"*". Among 

 these recombinants, only 0.2% are lysogenic. 



It is known that there exists a direct linkage between lysogeny and the 

 character GaU.^'- The extreme rarity of lysogenic recombinants, as well 

 as the considerable diminution of the proportion of Gal+ recombinants, 

 is the consequence of the spontaneous induction of the prophage in a 

 large fraction of the zygotes. The relatively smaller diminution of the 

 proportion of Lac"*" recombinants similarly reflects this phenomenon, 

 but shows at the same time that the character Lacj is much less linked to 

 the characters Gal 4 and ly than the latter are linked to each other. LaCi 

 is apparently located between TL and Gal 4. The localization of the 

 prophage in this region of the bacterial chromosome is demonstrated by 

 crosses of the type Hfr ly+ Lac+ TP X F" ly+ Lac^ TV, in which the 

 two lysogenic strains perpetuate different X prophages. The prophage of 

 the Hfr parent is transmitted to 30% of the recombinants while the Lac 

 and the TP characters are each transmitted in 50 and 75% of the cases. 



It should be noted that the establishment of the prophage of the Hfr 

 parent in the recombinants is one third as frequent as the development 

 of this prophage in the zygote in the course of crosses Hfr ly"*" X F~ ly~. 



It is known that in a cross of Hfr X F~ the high frequency of recombina- 

 tion observed concerns only the segment TL Lacj. We have verified this 

 fact in all of our crosses. The relatively high frequency of recombination of 

 the character X lysogeny thus localizes the X prophage in this segment. 



The elimination of a chromosomal segment by spontaneous induction 

 of the X prophage could also occur, though to an extent difficult to evaluate, 

 in crosses of the type ly+ X ly+ or F+ ly" X F" ly+. It offers a 

 model which might conceivably explain the segmental eliminations des- 

 cribed by J. Lederberg in heterozygote diploids^ and by W. Hayes* in 

 recombinants of Hfr strains. 



IF. Jacob and E. L. Wollman, Comptes rendus, 239, 317, (1954). 

 2E. L. Wollman, Ann. Inst. Pasteur, 84, 281, (1953); R. K. Appleyard, Cold Spring 

 Harbor Symp., 18, 95, (1953). 



3E. M. and J. Lederberg, Genetics, 38, 51, (1953). 

 4W. Hayes, Cold Spring Harbor Symp., 18, 75, (1953). 

 5J. Lederberg, Proc. Natl. Acad. Sci., 35, 178, (1949). 



335 



