LINKAGE RELATIONS IN MEN DELI SM 



113 



When, therefore, the F\ females are mated to yellow white males of 

 the genetic constitution (ywX}Y the progeny will give directly in its 

 phenotypic ratio the proportions in which the gametes are produced as 

 follows: 



49.45 gray white: 49.45 yellow red: 0.55 gray red: 0.55 yellow white. 

 The actual experimental results from this type of mating are summarized 

 in Table XXII. The actual linkage value obtained is 1. 13 which is substan- 

 tially the same as that shown in the previous table. On the basis of sum- 

 marized data of counts of 81,299 flies, Morgan and Bridges fix the value 

 for crossing-over between these two loci at 1.1 per cent. This is the value 

 we have used in deriving the above gametic ratios. Other factors have 

 been studied in the same way and give different percentages of crossing- 

 over. Thus Morgan and Bridges report the value for crossing-over 

 between white and miniature based on counts of 110,701 flies at 33.2 

 per cent., between white and vermilion from 27,962 flies at 30.5, between 

 vermilion and bar from 23,522 flies at 23.9, and so on for the whole series 

 of factors in the first group. 



TABLE XXII. FACTOR LINKAGE IN GRAY-RED FEMALE DROSOPHILAS OF THE TYPE 



(YwX)(yWX) 



Factors in the second and third groups display the same type of 

 linkage relations as those in the first group. As an example we may take 

 the recessive factors black and curved which lie in the second group. A 

 black curved female of the genetic constitution (6c v )(6c B ) crossed with 

 a gray normal male (BC V )(BC V ) gives in F\ gray long females and males 

 of the genetic constitution (BC v }(bc v }. When such F\ females are 

 crossed back to black curved males the results as reported by Sturtevant 

 and Bridges are given in Table XXIII. The observed percentage of 

 crossing-over between the loci B and C v in the second chromosome in 

 this experiment amounts to 24.04 per cent. 



When gray curved females (Bc v )(Bc v ) are mated to black normal 

 males (6C r ) (&(?) the F\ flies are gray normal as in the previous case, 

 but genetically they are of the constitution (<;) (6C r ). Such females 



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