GENE CONTROLLED PROCESSES I77 



first found that in mosaics most genes appear to be quite "autarchic,"^ 

 that is to say, they are not affected by the genetic constitution of neigh- 

 bouring tissue, but cause the small patch of tissue in which they are 

 located to develop the characteristic colour. This reveals nothing about 

 the nature of the gene reactions. Vermilion was an exception to the 

 rule; it was "hyparchic" to wild, that is, a vermilion patch in a wild eye 

 developed a wild eye colour. Ephrussi and Beadle^ have carried the 

 analysis much farther by transplanting imaginal discs of eyes of one 

 genetic constitution into larvae of different constitutions and observing 

 the colour of the eyes of the flies which develop. They have already 

 studied about twenty-six different genes, and their results can be most 

 easily summarized by relating them to the tentative hypothesis which 

 they have put forward. 



In this summary we shall deal only with the effects of the host on 

 the colour of the implanted eyes and neglea the much feebler effects 

 of the implant on the host. In a similar investigation on the moth 

 Ephestia,^ it has been shown that gonads containing the dominant 

 factor may have a considerable effect on the development of colour 

 when transplanted into a recessive host (p. 281). 



The transplantation work cannot reveal anything about the majority 

 of eye-colour genes, which are completely autarchic. In the non- 

 autarchic gene-reactions three substances are concerned: ca (claret) 

 substance, v (vermilion) substance, and en (cinnabar) substance. There 

 is a chain of reactions transforming ca into v and that into en substance. 

 This chain of reactions is brought about, not by the mutant genes as 

 the nomenclature might suggest, but by the normal allelomorphs. 

 Thus en substance is lacking in homozygous en eyes. It can be suppUed 

 by tissues of most other types, except those mentioned below, and if a 

 en eye disc is transplanted into a normal larva, it obtains en substance 

 from its host and develops wild pigmentation. Eyes homozygous for 

 V vermilion, em carmine, p^ peach or rh ruby have neither en nor v 

 substances, but these can be supplied if the eye discs are implanted 

 into hosts of any other constitution except claret. If a z; eye is grafted 



^ The word "autonomous" is usually used of the development of a gene 

 which is not affected by neighbouring tissues. There is at present, however, 

 no appropriate terminology for cases where interaction does occur between two 

 genetically different tissues. It may be convenient to use the terms "hyparchic" 

 and "eparchic," modelled on hypostatic and epistatic, and to use "autarchic" 

 in place of "autonomous." 



2 Revs. Beadle and Ephrussi 1937, Becker 1938, Ephrussi 1938, Ephrussi and 

 Beadle 1937. ^ K.uhn 1936, cf. Becker 1938. 



