SEX-LINKED INHERITANCE 435 
Usually no other sort of male is produced throughout the experiment 
except these two, but occasionally there is produced a male both 
yellow-bodied and white-eyed, or one which is gray-bodied and red- 
eyed, like wild flies. How do these arise? If in F, females the 
paired X’s were to exchange loads in part, so that G and R came to be 
attached to the same X and g and r to the other X, and if each of the 
flies Chromosomes 
xO XX Parents 
ry : } Gamete 
2X0: 2XxX F1 
3 9 
X 0 ¢ etes 
pets} one 
XX XX XO XO Fe. 
g é US 
Fic. 88.—Reciprocal cross to that shown in Figure 87. Parents, red-eyed 
male and white-eyed female; Fi, white-eyed males and red-eyed females (‘“‘criss- 
cross inheritance’—Morgan); F, equal numbers of red-eyed and white-eyed 
individuals of both sexes. The distribution of the sex chromosomes is shown at 
the right, as in Figure 87. (From Conklin, after Morgan.) 
eggs having such a constitution were to be fertilized with a sperm 
which lacked X (male determining sperm), this would make possible 
the production of F, males possessing both dominant characters and 
others possessing both recessive characters or gray-red and yellow- 
white respectively, as actually observed in about one case in a hundted 
by Morgan. 
It may add interest to the case to state parenthetically that in man 
occur a number of sex-linked variations which are inherited in this same 
curious fashion. Among them may be mentioned color blindness and 
