GENETICS OF BACTERIOPHAGE 



virus per cell were respectively 10, 250, and 1710. The yields of recombinants 

 were respectively 17, 29, and 42 per cent of the total virus. The yields of r-r+ 

 heterozygotes, however, did not differ significantly from two per cent in any of 

 the three populations. The proportions of the different segregating classes were 

 also the same among the heterozygotes in small samples from the first two yields. 

 This experiment shows that the interactions between phage particles giving rise 

 to recombinants (Doermann and Dissosway, 1949) and heterozygotes, are well 

 under way by the time infective virus begins to form in the cell. The rise in pro- 

 portion of recombinants during the latter half of the latent period, while the pro- 

 portion of heterozygotes remains constant, suggests that the formation and segre- 

 gation of heterozygotes may be continuing during this time. 



Summary of New Facts 



(1) When bacteria are infected with three kinds of phage carrying unlinked 

 genetic markers, about three per cent of the progeny carry markers derived from 

 all three parents. 



(2) When bacteria are infected with two phages carrying allelic markers, about 

 two per cent of the progeny particles segregate during further growth to yield 

 both kinds of phage. This is true for five different r markers, and an h marker. 

 The particles segregating to yield r and r+ phage are conveniently studied because 

 they produce mottled plaques. 



(3) The mottle producers are not clumps of particles because they are in- 

 activated as single units of normal sensitivity by antiserum, heat, /3-rays, and 

 ultraviolet light. Artificially prepared clumps are inactivated as multiple units. 



(4) There is no indication that the mottling particles can multiply before segre- 

 gating. In view of facts (3) and (4), the segregating particles are called hetero- 

 zygotes for the specified marker. 



(5) When the parental phage particles are marked at both h and r loci, the pat- 

 tern of segregation shows the following characteristics: 



(a) About two per cent of the progeny are heterozygous for h, and about two 

 per cent for r. 



b) The particles heterozygous for a single marker form four classes of approxi- 

 mately equal size, segregating into h, hr; h, wild; r, hr; and r, wild; respectively, 

 respectively. Thus single heterozygotes yield one parent and one recombinant 

 with respect to the original cross. 



(c) When the two markers are linked, the double heterozygotes segregate to 

 yield the two parents of the original cross, never the two recombinants, and never 

 more than two kinds of phage. When the two markers are unlinked, these al- 

 ternatives cannot be distinguished. 



(d) When the two markers are unlinked or distant, heterozygosis for one 

 marker is almost independent of heterozygosis for the second, and the doubly 

 heterozygous class amounts to only three per cent of the total number of hetero- 

 zygotes. Thus in the crosses hr7 X wild-type and hrl X wild-type, which yield 

 respectively 20 and 40 per cent of recombinants, the pooled heterozygotes segre- 

 gate to yield about 48 per cent of recombinants. 



189 



