THE MUTATED GENE 145 



allelomorphic series have been studied. The case that started 

 such deliberations has already been discussed, viz., the sex races 

 of Lymantria, where the actual dosages 1 and 2 are known and 

 the series of alleles fits in between in an orderly way. A similar 

 case has been worked out by Stern (1928, 1930) in connection 

 with the different quantities of the Bobbed gene in Drosophila, 

 the effects of which were reported on page 136. In this case, a 

 number of alleles of the Bobbed gene (bb) in the X- and Y-chromo- 

 some were found, called, in Stern's terminology, X 66 , Y bb ', X bbl , 

 X w . All of these have a different effect upon bristle length. 

 From the different combinations that may be built up Stern 

 estimated the relative activity of these alleles and found the 

 series 



+ = 30 

 Y bb ' = 10 

 X hb = 8 



ybb" _ 4 



X»i = 2 



It is now possible to make series of combinations of these 

 alleles together with dosage differences, as reported above. The 

 result is that dosages and alleles fit together perfectly in their 

 respective effects in all combinations studied. Figure 30 repre- 

 sents these results as a curve, in which the ordinate indicates 

 length of bristle (III normal, I very short) ; the abscissa gives the 

 different combinations of alleles and dosages arranged according 

 to the values calculated for them from the preceding figures. 

 The curve coincides with the assumption that the alleles repre- 

 sent dosage differences. 



In discussing these facts, it has to be kept in mind, however, 

 that multiple alleles may be of a very different type; a trans- 

 location with visible effect at the same locus as a known mutation 

 acts as an allele, though both actions may have a completely 

 different base. The same applies to deficiencies. But this 

 again leads to the problem of the theory of the gene. 



The questions put at the beginning of this chapter (page 125), 

 then, may be answered thus: 



1. Facts are known that prove that the gene (or chromosome 

 segment) may act, ceteris paribus, proportionally to its quantity. 



