10 PHYSIOLOGICAL GENETICS 



by action of ultraviolet rays abnormal abdomen in Drosophila, 

 resembling the well-known imitation. 



We have mentioned the fad that occasional phenocopies arc 

 found in many cases, apart from the systematic experiments just, 

 reported. One of these may be reviewed here because it belongs 

 to a case of special genetic and embryological interest. Another, 

 the experiments of Kuelm and Henke on the flour moth, will 

 be reported in the following chapter. 



A well-known hereditary abnormality in fowl is rumplessness, 

 which has been studied genetically and anatomically by Du 

 Toit (1913), Dunn (1925), and Landauer (1928). It consists of 

 a nidi mentation of the end of the vertebral column (see page 26). 

 ( Occasionally also in normal strains individuals are found who 

 exhibit this character in a nonhereditary form (about 1 in 1,000 

 individuals). Danforth (1932) succeeded in producing this type 

 as a phenocopy in 7}^ per cent of eggs treated with varying 

 abnormal temperatures during the first week of incubation. As 

 an explanation he accepts Stockard's views, which will be reported 

 on page 47. 



There can be no doubt that similar facts will be found in plants. 

 Numerous examples are known of modifications resembling 

 hereditary types. No systematic attack upon the problem, using 

 known gene mutations, is known, though it might be easily done 

 for floral abnormalities, leaf forms and types, and the like. 

 A hint at such facts is found in Zimmermann (1934). 



For curiosity's sake it might finally be mentioned that even 

 certain details of chromosome behavior fall into this group: 

 Genes are known that prevent synapsis of the chromosomes, and 

 the same phenomenon may be produced by action of abnormal 

 temperature (Oehlkers, 1936). There are genes causing abnormal 

 fertilization with consequent gynandromorphism (Goldschmidt- 

 Katsuki, 1927), and the same effect may be produced by tem- 

 perature shocks (Roesch, 1928). 



B. Related Phenomena 



Thus far we have recorded the cases in which the phenocopies 

 of different type were produced from the Wild type. There is 

 another group of experiments, also performed on Drosophila, in 

 which the phenotype of quantitatively different members of a 



