Wihm^— Simplified Solutions of Certain Mendelian Prohlems. 489 



There is another kind of comb carried by a Dutch breed of fowl, called 

 the Breda, which is described as having " ostensibly no comb. As a matter 

 of fact, in the cocks there are two minute papillae standing one on each side of 

 the middle line, which are rudiments of a comb structure. As experiment 

 shows, the hens have the duplicity of which these papillse are the evidence, 

 but in examination of the heads of hens practically no comb-tissue can be 

 seen or felt." Yet these combless fowl carry a factor which suppresses the 

 effects of other factors and another which lias the effect of splitting real 

 combs in two. 



The Breda comb was mated with both rose and single combs. When 

 mated with the single comb their liybrid had " a large double comb formed 

 as two divaricating singles." From tliis result four factors can be assigned 

 to the single comb and four to the Breda. The single comb is already known 

 to carry the characters x and y ; but, since it produces a real comb when 

 mated with the rudimentary Breda, it must carrj'- a factor for the pro- 

 duction of a real comb whioli is dominant to a factor for the rudiment of a 

 comb in the Breda ; and, since it produces a split comb when mated wil h the 

 Breda, it must also carry a factor for an unsplit comb which is recessive 

 to a factor for producing a split comb in the Breda. If we designate 

 these new pairs of characters B = real comb, r = rudimentary, S = split, 

 and s = unsplit, then the cliaracters carried by the single comb are now, 

 xyRs. The Breda comb carries the characters r and *S^, and it must also 

 carry x and y, for, did it not do so, its hybrid with a single comb would have 

 been somethiug else than a single. 



Thus there are now four pairs of characters connected with fowls' combs, 

 and the full set of sixteen groups of hybrids' progeny raiglit be set out with 

 the kind of comb belonging to each combination predicted. 



When the Breda comb was mated with the rose comb, " the resulting 

 combs were all duplex roses." Here again the two previously unknown 

 dominants are brought to light, namely, that for a real comb carried by the 

 rose comb, and that for splitting which must have been carried by the Breda 

 comb. When the hybrids were bred from, their progeny were counted into 

 six groups only, but, as there were more than four groups, there must have 

 been at least eight real groups, some of which were inseparable through the 

 action of the suppressing rudimentary factor brought in by the Breda. The 

 rose comb carries the factors XyBs, the Breda comb the factors xyrS. Thus 

 the two differ in three pairs of characters, and their hybrids' progeny should 

 have consisted of the eight groups which can be formed by combining the 

 three pairs of characters X and x, R and r, and S and s, in all the ways 



SOIENT. PEOC. K.D.S., VOL. XIV., NO. XXXVI. 4 H 



