Genie and Non-genic Parts of the Chromosome 89 



of pod factors. (9) We have mentioned the remarkable effects of 

 the Y-chromosome upon the pod effect: in one Hne, pod K, the females 

 do not show the effect except when they have an extra Y. In all 

 lines the addition of an extra Y or part of one changes penetrance 

 and expressivity, usually in different directions in the two sexes. (10) 

 There are remarkable relations to dominant Beaded: ordinary Bd 

 does not enhance pod, but one allele, Bd^, enhances one pod type 

 greatly. Also, the presence of pod increases the penetrance of Bd 

 itself; the strangest interaction of all is that in which Bd replaces the 

 action of an extra Y in pod K (point 9). (11) Another strange feature 

 is that in a pod line, pod H, the main pod factor simultaneously 

 causes a high incidence of chromosome elimination. The same factor 

 has also a maternal effect; that is, it acts upon the egg cytoplasm 

 before fertilization. (12) An unusually high incidence of pod factors 

 was found in the Minutes, themselves suspected of being hetero- 

 chromatic. 



All these facts lead us to the conclusion that we are dealing 

 with heterochromatic heredity. It seems rather remarkable that one 

 of the features, the false allelism of the pod factors in different 

 chromosomes, parallels the cytological behavior of intercalary hetero- 

 chromatin, namely, its unspecific attraction. The essential sameness 

 of mutant effects, their false allelism, their ubiquity, their interrela- 

 tions with Y heterochromatin, and their affecting early embryonic 

 differentiation suggest their being a part of an indispensable, inte- 

 grated, somehow generalized part of the genetical material, all of 

 which points to the intercalary heterochromatin. Needless to say, 

 this conclusion is based upon circumstantial evidence. A direct proof 

 or a decisive test is not yet available. 



There is some remarkable, though not completely clear, work 

 by Mampell (1945, 1946) with D. persimilis which shows some 

 interesting parallels to our podoptera work. He describes a recessive 

 "mutator," a locus in the second chromosome, which produces somatic 

 mosaics mostly of the Minute type. Sometimes the germ cells are 

 affected, and hereditary Minutes over all the chromosomes result 

 which are mostly deficiencies; also chromosome elimination is ob- 

 served, both very much hke the pod action in pod H, and similar in 

 percentage. Females do not show the effect, but addition of an extra 

 Y makes it appear, again, a close parallel to pod K. Mampell, there- 

 fore, thinks of a heterochromatic action, though he overlooks the 

 intercalary heterochromatin. It cannot be doubted that all the facts 

 reported thus far together make a strong argument, though there is 



