No. 639] INHEBITANCE OF BLUE IN POULTRY 323 



splashed or blacks. The breeder therefore prefers to use 

 for breeding purposes only those individuals which sliow 

 the desired phenotypic condition, even though so doing 

 necessitates the discarding of approximately half the 

 offspring. While this leaves a comparatively small num- 

 ber of individuals, as compared with other breeds, upon 

 which to practise selection, the blue Andalusian at least, 

 is bred in considerable numbers, thereby indicating its 

 economic desirability and its attractiveness. 



As was pointed out in tlie earlier paper (11)18, p. Ill) 

 if R and E are not at identical loci on h()moh)gous chromo- 

 somes and crossover individuals were found which ])ro- 

 duce RE gametes, the problem of the constant-breeding 

 blue would be solved. 



The situation regarding' black in rats may not be with- 

 out its bearing in the present case. Black rats which 

 bred true have been knowii for some time. Casth' (1!)1S)) 

 has, how^ever, reported certain races of bhicks whicli 

 failed to breed true. Tliis type of black was tested 

 through several generations by Casth' Ibsen 

 (1920) and Dunn (1920). Blacks mat.'.! t.. hhu-k^ <\u\te 

 persistently produced whites, blacks and icd • > . d _\ rlinws 

 in the ratio of 1 to 2 to 1. Castle (]911») lonii<l one i)os- 

 sible cross-over individual which died without being 

 tested. Ibsen (1920) has so far failed to find any, and 

 Dunn (1920) reports between one and two per cent, of 

 cross-overs. These cross-overs, whicli were longer 

 sought for and among larger numbers than li.is yot Ix-en 

 possible with. Andalusians, would api)c;ii' !<• m.-iki- ;i pos- 

 sible to sjTithesize a true breeding (/.'.. h<.iiin/\ i^ou^) 

 black, from the line which has not bet'ii ])reiM]iiii;- true 

 through a considerable number of generations. 



It is also worth noting in this connecti(m the possibh' 

 bearing of Sturtevant's (1919) finding families of 

 Drosophila carrjang at least two definite factors in the 

 second chromosome which almost eo!ni)letely inhibit 

 crossing-over in the region contiguous to \ hv\v loci. 



