122 



GENETICS IN RELATION TO AGRICULTURE 



TABU: XXV. CLASSIFICATION OF FACTOR COMBINATIONS TRANSMITTED BY FEMALES 



OF DROSOPHILA HAVING THE GENETIC CONSTITUTION 



(ywA 'biC,vm*rfb'X) ( Yvfa'Btd VMSRFB'X) 



No crossing-over 



186 



200 



3S6 



Growing-over between the loci 



Number of 

 yellow flies 



Number of 

 gray flies 



Totals 



Yellow and white 2 



White and abnormal 3 



Abnormal and bifid 4 



Bifid and club 17 



Club and vermilion 46 



Vermilion and miniature 7 



Miniature and sable 18 



Sable and rudimentary 28 



Rudimentary and forked 



Forked and bar 



Total single cross-overs 



Double crossing-over 



Y and W : C t and V 1 



Y and W : M and S 



Y and W : S and R 1 



Y and W : R and F 1 



W and A' : C t and V 1 



W and A' : R and F 1 



A' and B> : C t and V. . 



A' and Bi : S and R 1 



Bi and Ci : M and 5 1 



Bi and Ci : S and R 4 



Ci and V : V and M 



Ci and V : S and R 7 



Ci and V : R and F 2 



C t and V : F and B' 1 



Total double cross-overs. . 



5 



5 



11 



27 



51 



9 



19 



38 



5 



1 



7 



8 



15 



44 



97 



16 



37 



66 



5 



1 



296 



Totals 



30 



Interference. Interference is merely a consequence of the sectional 

 mode of chromatin interchange between homologous chromosomes. The 

 term is used to designate the observed fact that when crossing-over takes 

 place at a particular point in the chromosome the regions for some dis- 

 tance on both sides are protected from coincident crossing-over. The 

 operation of interference is well illustrated in Muller's data, although 

 the numbers are not sufficient to warrant a quantitative determination of 

 its effect. With long distances interference decreases, which is in accord- 

 ance with expectation. Even for relatively long distances, however, as 

 for the loci W, M and B f which we have already considered in detail 



