98 Colour and Other Characters in Pigeons 



and that colour requires a factor C, alleloiiiorphic with its absence c, 

 and further that S and P are neither of them completely dominant 

 (epistatic) over the other, we get the following zygotic types, opposite 

 each of which I put the pattern which it may be provisionally assumed 

 to represent : 



SS pp CC, SS pp Cc Black 



SS Pp CC, SS Pp Cc Black with grey webs 



SS PP CC, SS PP Cc i , , , . , , .^ .. ^, 



„ „ ^ Black with some white leathers 



Ss Pp CC \ 



Ss PP CC, Ss Pp Cc Black with white 



Ss PP Cc aud all combi- j 



nations containing P \ White with black 

 and C but not S ) 



That is to say, birds homozygous for S are black, with or witliout 

 grey webs or very few white feathers according to whether P is present 

 or absent. Birds heterozygous for S but containing P are in general 

 black with white, but if homozygous for P and hetei'ozygous for S 

 (Ss PP Cc) they may have preponderance of white. Birds without S but 

 containing P and C are white with black. 



If this scheme at all approaches the truth it explains (1) the 

 absence of whites in five matiugs (C 6'a //, C Ca III, G CalV, N, and Cb) 

 made between birds witli excess of colour over white (18 coloured, no 

 white). (2) The excess of whites in families where they occur is also 

 explained if it is assumed that a bird is white which contains C but not 

 S nor P (ss pp CC, ss pp Cc). If this is so, such a bird cros.sed with 

 a white containing S or P but not C, should give coloured offspring. 

 I have not been able to test this suggestion, but Staples-Browne in 

 crossing a White Fantail with a White Tumbler got a coloured F^. 

 His suggestion is that the Fantail was a dominant white, but the 

 explanation here suggested would lead to the same result. 



In conclusion, it should be mentioned that there was no evidence in 

 my experiments that the two young hatched from the same pair of 

 eggs are more often alike than young from the same parents out of 

 different nests. 



