38 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



Table 11. — Pi eosin sable 9 X vermilion cfcf • Fi tvild-type 9 9 X Fi eosin 



sable cfcf. 



If we consider the male classes of table 11, we find that the smallest 

 classes are eosin vermilion sable and wild type, which are the expected 

 double cross-over classes if sable lies to the right of vermilion, as indi- 

 cated by the crosses with eosin and with yellow. The classes which 

 represent single crossing-over between eosin and vermilion are eosin 

 vermilion, and sable, and those which represent single crossing-over 

 between vermilion and sable are eosin and vermilion sable. These 

 relations are seen in diagram II. 



w V « 



:x: 



X 



w ^ s 



Diagram II. — The upper line represents an X chromosome, the lower line its mate. 

 The cross connecting lines indicate crossing-over between pairs of factors. 



Non-cross-overs 



Single cross-overs 



Double cross-overs 



w= 



we 



w 



we 



V 

 V 



_s /Eosin sable. 

 \Vermilion. 



/Eosin vermilion. 



^ s ISable. 



I f Eosin. 



V s \Vermilion sable. 



I V I s /Eosin vermilion sable. 



^ *~ \WiId-type. 



If we consider the female classes of table 11, we get information as to 

 the cross-over value of eosin and sable, namely, 42 units. The male 

 classes will be considered in connection with the cross that follows. 



The next experiment involves the same three gens which now enter 

 in different relations. A double recessive, eosin vermilion (gray) female 



