H4 Experimental Zoology 



(c) Tortoiseshell 9 by orange $ 



(d) Orange 9 by orange $ 



(e) Orange 9 by black or blue $ 

 (/) Black or blue 9 by orange $ 



In all of these matings, in addition to tortoiseshell, kittens of 

 other colors may appear, viz. : 



(a) Tortoiseshell 9 by tortoiseshell $ gives tort., orange, black. 



(b) Tortoiseshell 9 by black or blue $ gives tort. 9 , 

 orange $ , black $ , 9 . 



(c) Tortoiseshell 9 by orange ? gives tort., orange, black. 



(d) Orange 9 by orange $ gives either tort., orange (or 

 blue) or only orange. 



(e) Orange 9 by black $ gives tort., 9, orange $ . 



(/) Black 9 by orange $ gives tort., black (and probably 

 orange). 



(g) Black 9 by black $ gives only black (or blue). 



From these results it appears that tortoiseshell is a heterozy- 

 gous color produced by the meeting of orange and black gametes. 

 The explanation that tortoiseshell cats are nearly always females 

 and rarely males is owing to orange nearly always dominating in 

 the male over black, while in the female the dominance of the 

 orange is incomplete, so that tortoiseshell results. In other 

 words, in the female sex the orange and the black both exist to- 

 gether, while in the male sex the yellow usually dominates. A 

 few examples will make the conclusion clearer. For instance, 

 in mating (e) when an orange female is crossed with a black 

 male, only tortoiseshell and orange kittens are produced ; if both 

 the orange and the black breeds are "pure," the female offspring 

 are tortoiseshell and the males yellow. In the reverse mating (/), 

 where a black female is crossed with a male orange, the male may 

 be heterozygous (i.e. having both black and orange germ-cells), 

 hence black kittens may also be produced. The kittens will be 

 black males or females, tortoiseshell females, and orange males. 



When a tortoiseshell female is mated with a black male, the 

 male offspring will be orange, because the tortoiseshell is hetero- 



