MENDELISM 



CHAP. VII 



suppose that the dominance of the horned character 

 depends upon the sex of the animal that it is 

 dominant in the male, but recessive in the female. A 

 pretty experiment was devised for putting this view to 

 the test. If it is true, equal numbers of gametes with 

 and without the horned factor must be produced by the 

 Fj ewes, while the factor should be lacking in all the 

 gametes of the hornless F 2 rams. A hornless ram, 



Dorset Suffolk 

 Ram Ewe 



.' x 9 



Suffolk Dorset 

 Ram Ewe 

 f 



x 9 



(FJ 



$-xd 



i r 



9 9 



FIG. 16. 



Scheme to illustrate the inheritance of horns in sheep. Heterozygous males shown 

 dark with a white spot, heterozygous females light with a dark spot in the centre. 



therefore, put to a flock of F T ewes should give rise to 

 equal numbers of zygotes which are heterozygous 

 for the horned character, and of zygotes in which it is 

 completely absent. And since the heterozygous 

 male's are horned, while the heterozygous females 

 are hornless, we should expect from this mating 

 equal numbers of horned and hornless rams, but only 

 hornless ewes. The result of the experiment con- 

 firmed this expectation. Of the ram lambs 9 were 

 horned and 8 were hornless, while all the i i ewe 

 lambs were completely destitute of horns. 



