THE MUTATED GENE 



237 



tive names. Figure 48 shows for 15 alleles which bristles are 

 affected by the respective genes. The fact that such an arrange- 

 ment is possible demonstrates a certain order in the scute effect, 

 i.e., a pattern, and in addition an orderly behavior of the different 

 patterns. This latter order is brought out in the experiments 

 of the Russian authors who analyzed all the possible compounds 

 of these alleles and found that the compound always showed only 

 an effect upon those bristles common to both types entering the 



Fig. 48. — The step allelomorphism of the scute alleles. Abbrev. as in Fig. 47. 

 mr, microchaetes on thorax; vs, ventral bristles; ex, coxals; w, crumpled wings. 

 {From Dubinin and Friesen, 1932, Zeitschr. Biol. Zentralbl. 52.) 



compound. This led to the arrangement as figured, which has 

 been called a step arrangement. 



There is, of course, no sense in analyzing this case from the 

 standpoint of pattern production, if these primary facts do not 

 hold. They have been accepted as valid by Sturtevant-Schultz 

 (1931), though their seriation is a little different. In recent 

 papers, G. Child (1936), however, doubts if there is a problem of 

 pattern involved at all. He bases this conclusion upon the 

 following facts. In temperature experiments on one scute line, 

 each bristle reacts independently of every other; it is determined 

 independently for each bristle whether it will be present or 

 absent. Flies raised at 14° show variations of some bristles, the 

 same bristles being constant at higher temperatures, and vice 

 versa. Such flies raised at different temperatures appear as 

 different from each other as do two different scute alleles raised 

 at the same temperature. From this he concludes that the 

 appearance of a pattern is an illusion, produced by looking 

 at the statistical differences in mean numbers instead of at the 

 condition of the individual fly, in which the distribution of bristles 

 may differ from that of any other individual. 



