THE M ( TA TED GENE 87 



Many more variations are imaginable, all of which may be 

 explained by the action of a single process occurring at different 

 rates. There is an interesting fact to be mentioned in this 

 respect. We remember that most of the mutant characters of 

 Drosophila, including also rnultiple-allelomorphic series, could be 

 reproduced as phenocopies. Some such cases involved effects 

 which in the case of the actual mutant show pleiotropic phe- 

 nomena. Thus the series of the truncate genes in Drosophila 

 affects the wing in the series oblique — dumpy — truncate but 

 affects simultaneously the hairs on the thorax, which form a 

 vortex in different degrees. In Goldschmidt's experiments on 

 phenocopies, the types of the wing series up to dumpy could be 

 reproduced, but there w r as no vortex. This shows that the hair 

 character has a different sensitive period to temperature shocks; 

 i.e., different details of developmental procedure are involved. 

 (See the facts regarding different sensitive periods in pleiotropic 

 characters of the flour moth, page 246.) This agrees with the 

 facts on pleiotropic multiple allelomorphs and their explanation. 



There is another set of cases in which some of the characters 

 controlled by the allelomorphie series show parallel seriation 

 whereas others do not. To this belongs also the vestigial series 

 which we tabulated on page 80. In this table, w r e omitted 

 another trait, found by Mohr (1932), viz., a shortening of the 

 second wing vein which is observable in the medium and lower 

 members of the series. This character does not follow the same 

 seriation as the others. If we use the same arrangement of the 

 £><7-scries as in Table 7 (page 80), the percentage incidence 

 of the character in question seems haphazard: 100, 2.1, 100, 0, 

 8.8, 73.3, 0, 2.6. If we look at the details of Mohr's data, how- 

 ever, we find a rule: The three high percentages are the com- 

 pounds in which the No-wing allele is involved. No-wing has 

 also other peculiarities, for it is semidominant to Wild type and is 

 homozygous lethal. From this one might draw the conclusion 

 that here some special feature is involved which we do not under- 

 stand yet but which has nothing to do w r ith the general chain of 

 reactions involved in the series. 



The oldest and best analyzed example of this type is Wright's 

 analysis of the albino series in guinea pigs (1916, 1925). Here a 

 series of multiple alleles produces a progressive dilution of 

 pigmentation down to albinism. If the gene for black color is 



