June 16, 1911] 



SCIENCE 



939 



SEX-LIMITED INHERITANCK AND SEXUAL DIMOR- 

 PHISM IN POULTRY 



When a Barred Eock hen is bred to a non- 

 barred, e. g., black, cock, all the female off- 

 spring are non-barred, all the male barred. 

 This generation, then, is sexually dimorphic. 

 The offspring of the reciprocal mating is not 

 dimorphic, since all the offspring are barred. 

 For reasons which will appear in a moment, 

 I wish to repeat the usual formulse for this 

 case; B standing for barred; b for non-bar- 

 red, e. g., uniform black. 



Barred Rocks: male, Be? BJ; female, B ^ b 2- 

 Non-barreds : male, h^ h^; female, h^ b ?. 



A. Barred females by non-barred male gives in Fi, 

 barred males, H ^ h ($; gametes, B <? b cj ; 



and non-barred females, b (j* b $ ; gametes, b (j' b $. 



Inbred they give in F,, barred males, B c? b (^ ; 



non -barred males, b^J b<j'; 



barred females, B cJ b 5 ; 



non-barred females, b cf" b J. 



B. Non-barred females by barred male give in Fj, 

 barred males, B c? b (j' ; gametes, B jj' b c? ; 



and barred females, B cj b J ; gametes, B <j' b J. 



Inbred they give in F™, barred males, iB cJ 'B (S; 



of tv7o sorts, viz.,|B(^ b,^; 



barred females, B J' b 5 ; 



non-barred females, b cJ b J. 



Now barring is a dominant character. If, 

 however, it is treated as a recessive, i. e., pa- 

 tent only in the homozygous condition, some 

 suggestive results follow. In the first place 

 the Barred Eocks become sexually dimorphic 

 in respect to barring, for the male, being 

 homozygous, will be barred, but the female 

 being heterozygous will be non-barred. 

 Moreover, this dimorphism will continue in- 

 definitely in succeeding generations. 



When this hypothetical dimorphic breed is 

 bred reciprocally to a uniform black breed, all 

 the Fj offspring will be non-barred and the 

 usual signs of sex-limited inheritance will be 

 lacking. The F, generation, as shown under 

 A, will all be non-barred, and of those under 

 B only one fourth will be barred and these 

 all males. 



This hjrpothetical case offers a plausible ex- 

 planation of the mode of inheritance of sex- 

 ual dimorphism. However, this case, while 



possible, is probably simpler than any likely 

 to be encountered in actual experience. 

 Moreover, the greater the number of different 

 factors involved, the more the observed ratios 

 will obscure the hypothetical ratios. 



The following experiments are interesting 

 in this connection : 



First may be recorded the results of cross- 

 ing Brown Leghorns and Buff Plymouth 

 Eocks. The former's plumage or some of its 

 elements is known to follow a sex-limited 

 mode of inheritance. Of the mating Buff 

 Eock females by Brown Leghorn male only 

 chicks in the down are on hand, but they are 

 exactly like the chicks of the reciprocal 

 mating. The adults of this last mating are 

 reddish buff in both sexes without the usual 

 features of sex-limited inheritance. In F, 

 true buffs appeared and various other colors 

 (among them the Ehode Island red color) but 

 no true Brovra. Leghorns. The detailed theo- 

 retical formulation must await the results of 

 other matings, but compare under A above. 

 Chicks in the down of the mating F, female 

 by Buff Eock male are on hand. None of 

 these, unlike many of the Fi chicks, are 

 striped. The absence of striped chicks indi- 

 cates an absence of the heterozygous form. 



In the second place are to be recorded the 

 results of castration experiments on young 

 Brown Leghorns. Though not yet old enough 

 to show all the adult characters, the castrated 

 males are assuming the male juvenile plum- 

 age, which, it should be noted, is almost as 

 sharply differentiated from the female's juven- 

 ile plumage as the adult male's is from the 

 adult female's. The castrated females, on the 

 contrary, have already assumed a considerable 

 part of the male's juvenile plumage. 



These experiments indicate that a recessive 

 character, sex limited in inheritance, can, ac- 

 cording to the formulse given above, be util- 

 ized in an explanation of the mode of inherit- 

 ance of sex dimorphism. On the other hand, 

 a dominant sex-limited character, at least in 

 poultry, does not lead in this direction. 



While it is probable that the plumage of the 

 male Brown Leghorn is a homozygous re- 

 cessive, and the female heterozygous, it is 



