286 Criticism of Ilypotliesis of Liiikcujc and C'rossiii(/ Over 



Ab _ 1 cross-over _ f 20 7„ of Bc^_ 1 C. . _ j 20 7,^ of 



AB 4 non-cross-overs | cross-overs BG 4 N. C. O. [cross-overs 



Ac _ 2 cross-overs _An°/ ^'^ — 2 C. O. _ . 



AC ~ 3 non-cross-overs " *" /" M ~ 3 N. C. 0. ~ ' = 



^tr_ 3 CO. ^e _ 3 CO. ^ ^, 



^i) 2 N. C. O. '^ BE 2 N. C. O.' '^ 



^_ 4 CO. _,„,, 5/;^ 4C.0. _ 



AE ~ 1 N. C. O: ~ '^ BF 1 N7C. 6! '° 



i/= ^C,«- =1007 

 ^i' N. C. O. 'o 



Ccz_ ICO. _ D^_ lao^^ 



(7i) " 4 N. C. 0. ~ '" i>A^ 4 N. C. 0. '" 



Ge _ 2 CO. _,„„, /)/• 2 CO. _ 



C^~3N. C0.~ '= i)^^~3N.C0. '° 



cf 3ca _..., g/- ICO. _ , 



G~F'2¥7C70.~ '° EF 4N.C.0. ■" 



If we assume that a single chromosome may have twenty-six factors 

 arranged in a row, A...Z, then 



Ah 1 C O. Az_^ 2 5 C 0. 



~AB " 24 N. C O. AZ N. C O. 



The cross-overs in which ^4 alone is concerned would range from 

 4 '7 to 100°/ . In general we may say then that cross-overs and 

 non-ci-oss- overs would ocon- in this scheme, and that while the number 

 of cross-overs increases with the distance apart, the number of non- 

 cross-overs decreases. The percentage of cross-overs however is always 

 proportional to the distance apart of the respective fiictors. If in 

 addition to the chromosomes whose behaviour is traced in this scheme, 

 there are other chromosomes which do not cross, the jiercentages of 

 cross-overs become of course reduced, but nevertheless still remain 

 exactly proportional to the distances apart of the fixctors. 



This scheme, without further elaboration, appears at first sight to 

 substantiate the crossing over hypothesis, and one is somewhat sur- 

 prised to find that it has not been worked out in detail by Morgan 

 himself. 



