24 MENDELIAN SEGREGATION 



Chance meeting between these will give the results 

 shown in the next diagram (Fig. 12). 



In the table (Fig. 12) the four kinds of eggs are 

 represented at the head of the four vertical columns, 

 and the four kinds of spermatozoa at the left of each 

 horizontal row. In the squares the combination of 

 each kind of sperm with each kind of egg is repre- 

 sented, giving the ratio of 9 long gray: 3 vestigial 

 gray : 3 long ebony : 1 vestigial ebony. 



The F2 expectation may, of course, be derived more 

 directly as follows: There will be 3 long to 1 ves- 

 tigial. These longs will be both gray and ebony in 

 the ratio again of 3 to 1 ; hence 9 long gray to 3 long 

 ebony. Correspondingly, the vestigials will be both 

 gray and ebony, in the ratio of 3 to 1; hence 3 

 vestigial gray to 1 vestigial ebony. The result is the 

 same as before. 



If one of tw^o independent pairs of characters is 

 sex linked, the same scheme holds in those cases where 

 the recessive sex linked character enters through the 

 grandfather, but the ratio is different when the re- 

 cessive sex linked character enters through the 

 grandmother (viz., 3 :3 :1 :1), as is to be expected 

 from the mode of inheritance of white eyes taken 

 alone ;^ and here, too, the result conforms fully to the 

 chromosome scheme. 



Three factors can be worked out by means of the 



\ 



1 For example, taking white and red\ alone the ratio of the F2 is 

 1:1. But among the reds the ratio of gray to ebony will be 3 : 1 and 

 among the; whites will be 3 : 1. Hence the result 3 red gray, 1 red ebony, 

 3 white gray, 1 wliite ebony. 



