444 



SCIENCE 



[N. S. Vol. XXXVI. No. 927 



sumptions: (1) that the male is homozygous 

 for sex and the female heterozygous; and 

 (2) that a " spurious allelomorphism " may 

 exist with the consequence that certain sex 

 and somatic factors may not be present in 

 the same gamete. 



These two assumptions are unnecessary if 

 the eytologieal evidence that male and female 

 determining sperms are produced by the male 

 is regarded. The eggs may then be considered 

 to be all alike. The appearance of recessive 

 females in F^ may then be explained with the 

 assumption that the female-determining 

 sperms of the recessive male parent may sup- 

 press the development of dominant characters 

 in the resulting zygote, or it may be assumed 

 that these sperms lack something which is 

 necessary to the proper development of the 

 dominant characters even when the female 

 parent bears them. Whether this suppressing 

 power or the lack of something necessary for 

 the development of dominant characters is 

 connected with an accessory chromosome or 

 not, is not essential to the assumption. 



In the formulas which follow, the characters 

 of the blond ring-dove are designated by B 

 and those of the white bird by W. Female- 

 determining sperms are distinguished by a 

 subscript ( with an additional ,v in the case 

 of those which are produced by the white 

 (recessive) male. It seems more appropriate, 

 and less confusing, also, to call all sperms male 

 and all eggs female, whether two kinds of 

 either exist or not, instead of using the signs 

 of both sexes, as is done commonly, for the 

 gametes of the sex which is considered to be 

 heterozygous. Characters which are recessive 

 to others, in the same individual, are included 

 in parentheses. 



X 



Blond ring-dove 



females 



1. Blond ring-dove White ring-dove 



males females. 



composit ion 



. Bd-BC?) W?W(c?) 

 producing ( Bj? 

 gametes ) B(c? 

 result: Blonds, Blond females, a few. 



mostly males 

 Be? (W?) B? (Wd") 



all W$ 



BJBCc?) 



2. White ring-dove 

 males 



compositio7i 



Wd-wc?) 



producing 



gametes 1 Wnvc? 

 result: Blond males Whit'e females 



Be? (W?) W,v$B(<?) becoming 



W?W(c?) 

 through presence of 

 condition indicated by 

 subscript w. 



Blond females, occa- 

 sionally, through ab- 

 sence of w effect. 



As the white F, hybrids were all females, it 

 was not possible to breed white hybrids inter 

 se. When these white hybrids were crossed 

 back on stock white males, only white ofi- 

 spring were obtained, and they were found to 

 be so-called extracted recessives. 



3. Blond Fi hybrid White ring-dove 



ring-dove males ^ females. 



composition 



Bc?(W$) W?W((?) 



r Be? 



producing J Brj? 



gametes 1 W^? 

 [ W,.c? 

 resutt: Blond males Blond females 



Be? (W?) B2 (Wc?) 



White males White females 



Wc?W(S) W$W(c?) 



4. Blond Fi ring-dove Blond ring-dove 



all W$ 



X 



females. 



all B2 



hybrid males 

 compositio7i 



Be?(W?) B$B(e?) 



r B^ 



producing I Btj? 

 gametes 1 W^J 



[ Wrwe? 



resiilt: Blond males Blond females 

 Bd'B(?) B$B(t?) 



and also White females 



Be?(W?) B5W,„(e?) becoming 



W?W(c?) 



through presence of 

 condition indicated by 

 subscript IT. 



