[Reprinted from SCIENCE, N. S., Vol. XXXV., No. 897, Pages 375-377, March S, 1912] 



HORNS IN SHEEP AS A TYPICAL SEX-LIMITED CHARACTER 1 



SEVERAL years ago Wood (1905) published 

 a note in -which, he showed that, in a cross be- 

 tween a Dorset Horn and a Suffolk (belong- 

 ing to a hornless breed of sheep), the male 

 offspring all developed horns but the female 

 offspring remained hornless. He showed 

 further that in the F 2 generation hornless 

 males arise, and these do not carry the de- 

 terminer for horns, and horned females, but 

 only when they have the determiner duplex. 

 Bateson (1909, p. 173) has discussed these 

 facts and drawn the conclusion : " Sex itself 

 acts as a specific interference, stopping or in- 

 hibiting the effects of a dominant factor, and 

 it is not a little remarkable that the inhibi- 

 tion occurs always, so far as we know, in the 

 female, never in the male." He admits, how- 

 ever, the difficulty in distinguishing between 

 this probability and the other possibility; viz., 

 that the male provides a stimulating factor. 

 Castle (1911, p. 102) concludes that the rea- 

 son horns are more strongly developed in 

 males than females is "the presence of the 

 male sex-gland in the body, or rather prob- 



1 Joint contribution from the New Hampshire 

 Agricultural Experiment Station and the Station 

 for Experimental Evolution, Carnegie Institution 

 of Washington. 



ably some substance given off into the blood 

 from the sex gland, favoring growth of the 

 horns " ; and he adds that if the male Merino 

 sheep (in which, usually, the male, and the 

 male only is horned) is castrated early in life 

 no horns are formed. He gives no reference 

 for the last statement; and in view of thep- 

 variability of the horned condition in the 

 males of the " Merinos " the conditions of the 

 experiments would have to be carefully con- 

 sidered before such a result could be accepted 

 as settling the question of the dependence of 

 horns in heterozygous males upon a secretion 

 from the testis. 



The hypothesis that we have adopted and 

 which works with entire satisfaction assumes, 

 first, that, as in man so in sheep, the male is 

 heterozygous (simplex) in sex. One sex- 

 chromosome is then to be expected in the male, 

 and substantially this condition has been 

 found to hold for man by Guyer (1910). The 

 female will then be duplex in respect to sex. 

 One further assumption is necessary; there is 

 an inhibitor to horn formation, and this is 

 located on the sex chromosome; consequently 

 it is simplex in the male and duplex in the 

 female. Thus it belongs to the well-known 

 class of sex-limited characters. The inhibi- 



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