No. 613] 



INHERITANCE IN FANTAIL PIGEON 



13 



concerned. The carriage of most of the birds was notice- 

 ably much more like the fantail than that of the F 1 and F 2 

 birds. 



Number of Factors Involved 

 The recovery of a certain number of the normal 12- 

 feathered tail in the F 2 might seem to furnish a basis on 

 which to calculate the number of factors involved; but 

 the fact that a few 12-feathered birds appear in Fj shows 

 that some, at least, of the heterozygous combination are 

 included in the F 2 twelve feather group. It is also pos- 

 sible, even probable, that other F 2 combinations may also 

 fall within this group. It is impossible, therefore, to ar- 

 rive at anything more than a possible conclusion from 

 the F 2 data because the relative value of the heterozygous 

 classes can only be guessed at. 



Two factors will obviously not fit the results, because 

 there would be expected more of the higher numbers of 

 tail feathers both in the back cross and in the F 2 count. 

 Three factors fit fairly well. Let A, B, C represent par- 

 tially dominant factors for fantails, and a, b, c their nor- 

 mal allelomorphs (aabbcc being the normal 12-feathered 

 tail). In the F 2 there will be expected only one pure 

 fantail out of 64 (viz., AABBCC) and one pure 12-feath- 

 ered type (viz., aabbcc). There will be six F 2 classes with 

 only one dominant factor heterozygous for A or B or C. 

 These, theoretically at least, if all the factors have equal 

 efficiency, would be the most likely ones to fall within the 

 12-feathered group. If these include all of the expected 

 12-feathered tails in F 2 there should be seven 12-feath- 

 ered in 64. There were 278 F 2 individuals. On the same 

 calculation this would give- an expectation of only 10.5 

 twelve-feathered tails. But the F 2 records actually gave 

 46 normal tails. Obviously still other combinations 

 realized in F 2 must come under this class. It would be 

 mere guesswork to try to state which are the more prob- 

 able combinations. 



The back cross furnishes data that permit a better means 

 of calculation. Here eight kinds of germ cells and eight 



