164 



CELL HEREDITY 



(a) 



(b) 



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X 



y 



y 



X 



X 



X 



y 



X 



y 



164 



y 173 240 279 271 274 201 



(C) 



id) 



p = Recombination frequency 



FIGURE 6.5. Linkage maps of 74 phage (from Benzer, 1956, Mutation, Broot/ioven 

 Symp. Biology, 8:3). 



(a). The location of the rll region is shown. The inset shows the estimated cor- 

 responding spacing of nucleotides (circles) according to the structure of Watson and 

 Crick on the assumption that the phage "chromosome" is such a fiber of DNA. 



(b). The locations are shown of a number of rll mutants within the region. (There 

 is some distortion due to the difficulty of drawing lines suflFiciently close to one an- 

 other.) A horizontal line represents an "anomalous" mutant which produces no wild 

 recombinants in crosses with any mutant covered by its span. 



(c). A selected group is shown on larger scale. 



(d). Further magnification. 



