414 



EVOLUTION, GENETICS, AND EUGENICS 



the reverse of that described for DrosophUa, so far as the sexes are 

 concerned; and this, interestingly enough, is exactly what we get. 



A typical instance of sex Unkage of this sort is seen when a Barred 

 Plymouth Rock cock is mated with a Black Lanshan hen (Fig. 82). 

 All offspring, both males and females, of the Fi generation are barred ; 



Fig. 83 — Reciprocal cross to that shown in Figure S2 P, parents, unbarred 

 male, barred female; Fi, barred males, unbarred females (crisscross inheritance); 

 Fj, barred and unbarred birds equal]}' numerous in both sexes. {From Castle.) 



but when the individuals of Fi are interbred (or the F, males are bred 

 with any barred females), all males are barred and half of the females 

 are barred and half are black. Here we see that the recessive char- 

 acter, black, is Hnked with the female sex. If we cross a black female 

 with an Fj male we can get equal numbers of barred and of black males 

 and females. The reciprocal cross (Fig. 83) illustrates crisscross in- 

 heritance. Starting with a black male and a barred female, we get in 

 Fi barred males and black females. When the Fi individuals are in- 

 terbred we get half barred and half black males and females 



