366 



CELL HEREDITY 



Strand 



3 



adie ads 



Grows on 

 minimal 

 medium 





paha 



29 0(0)11 



0.1 014 





ad 16 + 

 + + 



Grows on 

 minimal 

 medium 





paba 



- + 



+ ac's 



Will not grow 



on minimal 



medium 



iU 



paba 



ad 16 + 

 + adi 



Will not grow 



on minimal 



medium 



i 



paba 



- + 



+ 

 I ad 16 

 \ada 



Strand b c 

 cis 



bi - 



+ 

 ad 16 



-bi 



b d 



ado, 



I ad 16 

 lada 



>' I 



+ 



adyi 



I r I I I I 



ii I 



+ 

 ad 16 



\bi 



a d 

 trans 



FIGURE 12.6. Recovery of reciprocal recombination products from mitotic crossing 

 over in Aspergillus. The minimal medium in these experiments lacks adenine but 

 contains biotin (adapted from Roper and Pritchard, 1955, Nafure, 175:639). 



centromere in inverse proportion to the pro.ximitv of the intermediate 

 marker to that reference point. For example, if the order of genes is: 

 centromere, pro. paha. y. there should be (barring double exchanges) no 

 segregants homozygous for pro that are not at the same time homozyg-ous 

 for paha. Conversely, among the y/y homozvgotes there should be more 

 paha paha than pro/pro. If y were proximal to the other two genes, 

 then all |//(y homozygotes should also be homozvgous for pro and paha. 

 When markers linked with the one used for selection are recessive and in 



