THE GENE 



311 



Wright studied a multiple allelomorphic 

 series of a diluting gene for coat and eye 

 color, which may be combined with 

 different factorial constitutions of other 

 genes and produces in these combinations 

 closely parallel series of effects. This leads 

 him to the conclusion (Wright in Castle 

 and Wright, 1916, p. 71) that "it seems most 

 satisfactory to attempt to explain the results 

 on the basis of four quantitative grada- 

 tions of one factor, which determines the 

 amount of the basic color-producing 

 enzyme." In a recent publication ('2.5) 

 the same author returns to this subject and 

 concludes "that the factors of the albino 

 series determine the rate of some one 

 process fundamental to all pigmentation 



" The experiments of the 



present writer, which have led to the 

 actual demonstration of such curves of 

 velocity in a parallel case, have been 

 overlooked by this author, which makes 

 his work still more important as a verifica- 

 tion of our conclusions. 



This work of the present writer ('17, 

 'zob, 't-4) has enabled him to study the 

 effects of a multiple-allelomorphic series 

 of a gene on a character in different stages 

 of development. The characters in 

 question are the markings of the cater- 

 pillars in different geographic races of the 

 gipsy-moth, characters which can be 

 traced through the different stages of 

 development of the caterpillars. From 

 the manifold facts which the study of the 

 races and their crosses has brought to 

 light only those pertaining to the present 

 question may be mentioned. The two 

 extreme races are that with light-marked 

 caterpillars, retaining their pattern 

 throughout life up to the last instar, and a 

 darkly pigmented race not exhibiting the 

 pattern of light markings. Between these 

 stand other races which in young stages 

 show the light pattern, which however is 

 covered in the course of development with 



dark pigment so that grown up cater- 

 pillars of such races cannot be distin- 

 guished from those of the dark pigmented 

 races. We might call this the inter- 

 mediate type. Between this and the dark 

 races as well as the light ones many other 

 races are found showing the same type of 

 developmental change from light to dark 

 but in different degrees. Light and dark 

 are a simple pair of allelomorphs and all 

 the other intermediate types are based on 

 multiple allelomorphs of these genes. 

 This is not surprising as we know that 

 in the silk worm also many types of 

 markings form such allelomorphic series. 

 If now a light race is crossed with a dark 

 one the F x caterpillars are light in young 

 stages and become dark in later stages of 

 development, thus behaving exactly like 

 the pure intermediate races. If we plot 

 curves of the changes of pigmentation 

 during development in the different pure 

 races, dividing the scale from light 

 markings to no markings into classes we 

 get empirical curves of the progress with 

 time of pigment deposition in the skin of 

 the larvae. If this more or less increasing 

 deposition of pigment is the result of a 

 chain of reactions, these curves demon- 

 strate the typical velocities of the reaction. 

 (For details see the full presentation in 

 '2.4). If these empirical curves are plotted 

 for the pure races as well as their hybrids 

 we realize at once that the different 

 multiple allelomorphs of the pigmentation 

 factor have the effect of producing pigmen- 

 tation curves of different and specific veloci- 

 ties, the velocities of hybrids lying between 

 those of the respective pure races. Here 

 then we have first the exact demonstration 

 that such different states of a gene, which 

 are called multiple allelomorphs, produce 

 reactions of different and typical veloci- 

 ties; further a very strong intimation that 

 these multiple allelomorphic genes are 

 different quantities of the same gene, as 



