APPENDIX 2 



Standard type. Since most of these variants are due to recessive genes, the emphasis 

 is thus generally on the effect of the recessive allelomorph. For example, a gene 

 which causes a yellowing of the body colour is called yellow and designated by y. 

 Where, however, the effect of the mutant gene is detectable in the heterozygote, 



STRUCTURAL CHANGES ARISING FROM IRRADIATION, 

 CHEMICAL TREATMENT OR SPONTANEOUSLY (FROM 

 DARLINGTON AND LA COUR, 1945. /. Genet., 46, 180-267, 

 AND DARLINGTON AND KOLLER, 1947. Heredity, 1, 

 187-222) 



the gene is described as a dominant (though it may not be dominant in the 

 mendehan sense of giving a heterozygote indistinguishable from the mutant 

 homozygote). It is named from the appearance of the heterozygote and is given 

 a capital letter suggesting its name. Thus H indicates the gene Hairless which in 

 the heterozygous condition removes certain hairs from the fly, though when 

 homozygous it has a lethal effect. Two and even three letters are of necessity 

 sometimes used as symbols. Thus c— curved (wings), ca^= claret (eye colour) 

 and cflr= carnation (eye colour). 



In contradistinction to the earher system the wild-type allelomorph of a mutant 

 gene is not denoted by the same letter, but in different case, as that for the mutant. 



429 



