12 
SIDNEY I. KORNHAUSER 
male (red eyed) back to a recessive female (white eyed) and 
gives a 1:1 ratio. The females (which must have two X- 
chromosomes) all received an X-chromosome from their father 
and are red eyed. The males all received their single X- 
chromosome from their mothers and are white eyed. 
Red Eyed Female White Eyed Male 
XX X Y 
G-ametes and Combinations 
X X 
X Y 
F* 
X X 
Red Eyed Females 
Gametes and 
X Y 
Red Eyed Males 
Combinations 
F3 
(1) (2) (3) 
XX XX X Y 
Red Eyed Females Red Eyed 
Males 
(4) 
X Y 
White Eyed 
Males 
Fig. 4. Diagram Showing Sex-Linked Inheritance in Drosophila 
An underscored X represents an X-chromosome bearing the gene for red eye ; 
because this is dominant over white eye, any individual with an underscored X 
will have red eyes. 
This criss-cross type of inheritance has long been known in 
man. Color-blindness is perhaps the best known illustration 
and behaves in its inheritance exactly like red eye in Drosophila, 
That color-blind females are so rare is due to the fact that nor- 
mal color vision is dominant over color-blindness, thus XX and 
XX are females with normal color vision; but the latter is a 
carrier for color-blindness. XY is a normal male and XY a 
color-blind male. The mating of a female carrier with a color- 
