Genie Control of Development 399 



have just presented a model. This would be a purely physiological 

 interpretation, leaving out of consideration the nature of the multiple 

 alleles and considering only their actions and interactions. But a com- 

 pletely different type of interpretation has been proposed, namely, the 

 presence of a set of pseudoalleles, of which at least three (probably 

 more) are needed (Silow and Yu, 1942; Yu and Chang, 1948, quoted 

 from Stephens ) : one controHing pigment in the vegetative parts; one 

 for a white ghost spot at the base of the petals; and one which, to- 

 gether with the last, produces the basal spot on the petals. The differ- 

 ent effects of the allelic series are then a consequence of crossing over 

 between the pseudoalleles. We are not interested here in the details of 

 this explanation ( which is not accepted by Stephens ) , which, after all, 

 is the product of the tendency to circumvent difficulties in the explana- 

 tion of genie actions by distributing them among different genes (or 

 by splitting a gene into subgenes, as Stadler preferred). The point I 

 wish to make is to emphasize the difficulty of drawing conclusions 

 concerning genie actions when, in cases like those mentioned here, we 

 are not even sure whether or not we are dealing with simple events of 

 a type underlying all genie actions. 



In still another way the problem of pleiotropy touches the problem 

 of pseudoallelism. The eye-color locus vermilion (v) in Drosophila 

 may be said to be pleiotropic (though not in the usual sense of the 

 term), so far as v produces vermilion eyes and a condition which may 

 be reversed by the presence of specific suppressors. Green (1954) has 

 described pseudoalleles of v which produce the eye color but do not 

 react to the suppressors. From this he concludes that the two pseudo- 

 alleles are "different genes" and that my interpretation of pseudo- 

 alleles does not hold. He forgets that within a multiple allelomorphic 

 series, individual members may act differently as suppressors, as I 

 showed for the silver series (1945a). This situation is the reverse of 

 that in the v alleles, but it shows that suppressor actions as such 

 (active or passive) may differ among multiple alleles, which vitiates 

 Green's arguments. 



This subject may one day become important for the analysis of the 

 chromosomal basis of heredity. It is remarkable how many examples 

 of pseudoallelism as well as of accumulation of loci in a chromosomal 

 section are known to be connected with a pattern effect of a pleiotropic 

 type. We find this in the position effect sections of the Drosophila 

 chromosomes. The yellow position effect of a break within a well- 

 defined section (as studied above) may affect the entire body, which 

 is yellow, or it may leave the bristles partially or totally unaffected. 



