84 T. H. MORGAN AND ELETH CATTELL 



WByX - WByX White black 9 

 RbYX - WbY Red yellow & 



WByXRbYX Red gray 9 

 ^1 WByXWbY White gray d' 



WBYX - WByX - RbYX - RbyX Eggs 



Gametes ot i<i ^ygyx - WByX - WbY - Wby Sperm 



Gray white 9 3 Gray white d' 3 



Gray red 9 3 Yellow red d 3 



^ Black white 9 1 Black white c^ 1 



Black red 9 1 Brown red cf 1 



There were five cases of crossing-over of color factors in the 

 males, in a total of 2993 males; approximately, once in 600 

 times. The crossing-over was between Rb and WB. Each time 

 that the crossing-over occurs one way, there should be on an 

 average a counter-cross the other way. Thus, when an inter- 

 change between Rb and WB takes place the combination RB will 

 occur as often as Wb. We should expect, therefore, to find a 

 balance in the results, except in so far as accident or death 

 obscure the output. In the present case the cross-over RB sur- 

 vived four times (giving 3, LRN and 1, LRB), while the coun- 

 ter-cross Wb survived only once. Three of the counter-crosses 

 are not, represented. The result can probably be explained by 

 the lower viability that exists for the Yellow- whites. 



The reciprocal cross is given below. There were also eight 

 large classes but no cases of crossing-over. The numbers are 

 much fewer than in the last case. 



LRY 9 by LWB d 



LRN 9 = 255 

 ^' LRY d = 262 



