50 



POULTRY 



Comb- characters 



Relatioji of Rose-comb to Fea-co7nb 



In the preceding Report we showed 

 that, judged by the criterion of 

 gametic output, 4 kinds of r.p. birds 

 exist, viz., r. X p-, r.p. X r.p., r.p. X r., 

 and r.p. X p- Birds of the constitution 

 r. X p- gave, on mating with single 

 comb, equal numbers of the 4 types 

 r.p., r., p., and s. Birds of the consti- 

 tution r.p. r. and r.p. p. gave when 

 crossed with s. equal numbers of r.p. 

 and r., and of r.p. and p. respectively, 

 whilst a pure r.p. bird gave only r.p. 

 when similarly crossed. We suggested 

 that a fifth type of r.p. bird was con- 

 ceivable, i.e., one giving off equality 

 of r.p. and s. gametes. In order to test 

 this possibility a pure r.p. 9 was mated 

 with a single comb $ (Experiment 

 268). Three $s. resulting from this 

 cross were in the following year mated 

 with their father (Experiments 342 

 and 343). From these matings all the 

 4 types of comb resulted. In other 

 words, the gametic output of birds 

 produced by the union of r.p. with s. 

 cannot be distinguished from that of 

 birds produced by mating r. with p. 

 Judged, therefore, by gametic output, 

 only 4 types of comb are known to 

 exist. 



Since the publication of the last Re- 

 port we have been led to alter our 

 views as to the nature of the r.p. comb, 

 and have recently pointed out ^ that 

 the case may be looked upon as one of 

 simple dihybridism. On this view the 

 allelomorphic pairs are ( 1 ) Rose and 

 no-rose; (2) Pea and no-pea— the first 

 member of the pair being in either 

 case dominant to the second. The 

 rose-comb is, therefore, in constitu- 

 tion Rose + no-pea {R. no P.) and 

 the pea-comb Pea -\- no-rose (P. no 



BATESON AND PUNNETT 



R.). Consequently the zygote formed 

 by the union of r. and p. has the con- 

 stitution R. no P. : P. no R., and the 

 appearance of the walnut form must 

 be regarded as due to the presence in 

 the zygote of the 2 unit characters R. 

 and P. which belong to distinct allelo- 

 morphic pairs. From such a zygote 4 

 sorts of gametes must be produced in 

 equal numbers, viz., R.P., R. no P., 

 P. no R., and no R. ?J0 P. Since the 

 single on this view must be homo- 

 zygous and producing gametes of the 

 constitution no R. no P., it follows that 

 an r.p. bird such as we are considering 

 will, when mated with a single, give 

 rise to 4 zygotic types in equal num- 

 bers. Constitutionally these will be ( 1 ) 

 R. no R. : P. no P., (2) R. no R. : no P. 

 no P., (3) P. no P. : no R. no R., and 

 (4) no R. no R. : no P. no P., and visi- 

 bly such birds will be r.p., r., p., and 

 s. respectively. Again, when mated to- 

 gether, 2 such r.p. birds will produce 

 r.p., r., p., and s. birds in the ratio 

 9:3:3:1. The constitution of such 

 birds is set forth in the accompanying 

 table (p. 13), which shows that the r.p. 

 birds may be of 4 sorts, viz. ( 1 ) homo- 

 zygous for both R. and P.; (2) homo- 

 zygous for R. and heterozygous for 

 P.; (3) homozygous for P. and hetero- 

 z\'gous for R.; and (4) heterozygous 

 for both R. and P. The relative pro- 

 portions of birds belonging to the 4 

 classes (1), (2), (3), and (4) will be 

 1 : 2 : 2 : 4. As the table shows, one of 

 the 3 roses and one of the peas will be 

 homozygous. 



We have already pointed out - that 

 the. proportion of the different combs 

 in the various matings affords no cri- 

 terion for judging between this view 

 and the one previously suggested. The 

 new view, however, explains the iden- 

 tity of the combs produced by the 

 crossing of r. with p. and of r.p. with 



1 Proc. Comb. Phil. Soc, 13, p. 167. 



2 Loc. cit. 



