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THE AMERICAN NATURALIST [Vol. LII 



Such an interpretation makes the characters black and 

 blue-splashed the allelomorphs. 



The practise of referring to characters that seem to be- 

 have in an alternative relationship in heredity as allelo- 

 morphs, instead of factors occupying identical loci on 

 homologous chromosomes, is, it is to be hoped, passing. 

 That it has lead to a misinterpretation in the present case 

 is shown by the fact that all the offspring of certain pure 

 white birds mated with blue-splashed ones are blue. The 

 E factor must have come from an individual that was ho- 

 mozygous for it and devoid of pigment. It appears rea- 

 sonable to expect that among the F 2 's from the white 

 Wyandotte X blue-splashed Andalusian cross will appear 

 pure whites that carry the R factor. If this proves to be 

 the case the allelomorphs are two factors, R and E, which 

 act on black pigment. R arranges and restricts the pig- 

 ment in the feather structure so that it gives a bluish-gray 

 appearance. E extends any black pigment present to all 

 the feathers of the body. One and probably either or 

 both may be present without any phenotypic expression 

 whatsoever. In fact, for every sixteen F 2 individuals 

 from this cross four pure whites are to be expected in 

 which the genotypic ratio with regard to R and E is 1 : 2 : 1, 

 exactly as in the F 2 's from a cross of a black and a blue- 

 splashed Andalusian. One of these whites will be homo- 

 zygous for R like the blue-splashed Andalusian. One 

 will be homozygous for E like the black Andalusian. And 

 two will be heterozygous for E and R, as are the blue 

 Andalusians. But because there is no black pigment 

 present these differences in the genotype do not affect 

 the phenotype. For the sake of clearness the expectation 

 of this cross is shown herewith, carried through the F 2 

 generation. P is taken to represent a factor necessary 

 for the formation of pigment which is present in the blue- 

 splashed Andalusian, but absent in the white Wyandotte, 

 while E and R are represented as allelomorphic to each 



