August 9, 1912] 



SCIENCE 



191 



C(we II. 



Parents: <? 473 A, yellow 



$ 650 A, black baldhead 



I Offspring: 799 A, dun, ? 



799 B, dun, $ 

 841 A, black, c? 

 890 A, dun, ? 

 890 B, dun, 5 

 938 B, dun, ? 

 980 A, dun, $ 



A searcli of the records for other eases fur- 

 nishes abundant evidence to indicate that the 

 phenomenon is general, and under certain con- 

 ditions holds for the intense and dilute fac- 

 tors, -whatever the color concerned. The 

 requisite conditions appeared to be the mating 

 of a dilute male to a female showing the 

 intense condition. Further investigation 

 showed that this is a typical case of sex-linked 

 inheritance in that in stock bred pure for the 

 character in question one sex is always hetero- 

 zygous. In this case it is the female which is 

 heterozygous, the character involved being the 

 intense condition of pigmentation. In respect 

 to the sex concerned this character corresponds 

 to barring in the fowl and to color in Ahraxas, 

 and differs from color blindness in man and 

 the numerous sex-linked characters which 

 Morgan has found in Drosophila. These re- 

 sults have furnished a satisfactory explanation 

 of certain formerly disquieting records in 

 which birds bred "pure" and supposedly 

 homozygous for the intense condition have 

 produced some dilute offspring when bred with 

 heterozygous or with dilute mates. It is now 

 found that in aU such eases noted the birds in 

 question were females and, furthermore, that 

 all the dilute offspring, so far as at present 

 observed, were likewise females. A thorough 

 analysis of the subject is now being made and 

 the detailed results will be published in the 

 near future. 



The results mentioned above may be satis- 

 factorily represented by either of the accepted 

 modes of symbolism which have been employed 

 in similar cases. Without committing our- 

 selves to any theory, we may here follow the 

 usage of Spillman and of Pearl in explaining 



the inheritance of barring in poultry. In 

 these formulse F represents femaleness, and 

 the female is always heterozygous (Ff) with 

 respect to this factor. Males, on the other 

 hand, are assumed to lack this factor entirely, 

 and are accordingly homozygous jf. We may 

 then let B represent the factor for black, in 

 the absence of which (b) the bird is red. 

 These colors are modified, however, by the 

 presence or absence of I, the factor for the 

 intense condition. In the absence of / (repre- 

 sented by i) black becomes dun, and red be- 

 comes yellow. It is now necessary to make 

 only the further assumption that F and I 

 can not occur together in the same gamete. 

 The cases given may then be represented as 

 follows : 

 Case I. 



Parents: dun (? =fBi.fBi 

 black 2 = rBLrFBi 

 Gametes: cJ, all fBi 



?, fBI and FBi 

 Combinations: fBi-fBI ^hla-ek ^^ 

 fBi. FBi ^= dun ?? 

 Case II. 



Parents: yellow ^ = fM-fbi 



black ? = fBI. FBi 

 Gametes: ^, all fbi 



$, fBI and FBi 

 Combinations: /fci./BI=: black J^ 

 fbi-FBi=d.viii 2i 



It will be seen that these expectations accord 

 with the results obtained. 



It has been mentioned that this explanation 

 accounted also for certain unexpected results 

 from birds which were at the time supposedly 

 homozygous. A single example will suffice. 



Parents: c? 681 B, black 

 5 701 A, red 

 I Offspring: 846 B, yellow, J 



892 A, red, c? 

 892 B, dun, ? 

 944 A, black, c? 

 944 B, black ^ 



It was known from his ancestry that 681 B 

 was heterozygous, both with respect to B and 

 I. But had 701 A been homozygous for I, as 

 supposed, all the offspring should have shovm 

 the intense condition of pigmentation, namely. 



