176 Nature of the Genetic Material 



general system of the pattern and function of the genie material 

 of the chromosomes. In both interpretations, the problem of action of 

 the genie material enters, (We shall return to this in the proper 

 chapter.) In my opinion, the interpretation based upon the classic 

 gene and pseudoallelism requires quite a series of assumptions in 

 regard to the fate, location, sequence, and interaction of the reaction 

 products and, in addition, phylogenetic considerations as exemplified 

 in Lewis' elaborate discussion. In my way of looking at the facts, 

 any interpretation of genie action also covers the facts of the present 

 discussion. 



A final word about terminology. The term "pseudoallelism" has 

 had such wide acceptance that it can hardly be replaced, though 

 it implies a definite interpretation, just as the term "position effect" 

 does. Other terms proposed are "semi-allelic" (Muller, 1949; Komai, 

 1950 ) , "twin genes" ( Komai, 1950 ) , and "isophene segment" ( Kaplan, 

 1952). Laughnan (1952Z?) has proposed "pair-alleles," which he 

 thinks contains the notions both of close linkage and similar pheno- 

 typic effects. Of course he is considering the "anomalous" situation 

 of side-by-side arrangement of genes instead of the usual opposite 

 orientation. This would mean that a rare, not typical phenomenon is 

 involved, based upon duplication of a locus. He thinks that this view 

 does not necessarily require the particulate gene, but would also 

 work with our segments of mutant action. I have already expressed 

 my disagreement with such views. We shall see whether the term 

 "pseudoallelism" can still be replaced or will remain in spite of mis- 

 taken inferences, just as "position effect" and "cell" have remained. 



ff. On allelism 



In the present discussion the term "allelism" and its meaning 

 have played a considerable role. We may consider this phenomenon 

 basic for genetics and try to endow it with a definite meaning. As 

 a rule, we take allelism for granted. Genes appear in pairs of alleles. 

 Mendelian segregation as well as crossing over work with pairs of 

 alleles. So does the elementary cytological aspect of genetics in 

 which the synapsing points of the homologous chromosomes are in 

 some way identified with a pair of alleles. Also, the secondary 

 phenomena of Mendelism like dominance, dosage relations, defi- 

 ciencies, multiple alleles, and multiple factors deal invariably with 

 pairs of alleles, and so does any theory of mutation. Therefore it is 

 of fundamental importance to know what allelism means; this knowl- 

 edge, if acquired, would necessarily include the theory of mutation. 



