92 Nature of the Genetic Material 



Schmidt, 1923?;), which indicates at least the presence of heterochro- 

 matin. In DrosopJiila it was originally assumed that all autosomes 

 carry male determiners (Bridges, 1922). But the fourth chromosome 

 is ruled out because haplo- or triplo-IV does not affect sex. A care- 

 ful check of the second chromosome made by S. Bedichek Pipkin 

 (1947) with the translocation and triploid method failed to find any 

 major sex determiners, which, then, must be located in the third 

 chromosome. Some geneticists consider all mutant loci which can 

 produce a shift in sex (different types of intersexuality, abnormal 

 genitalia, sterility) as sex determiners, and such loci are found also 

 in the second chromosome. But a comparison with the facts in 

 Lymantria as well as Pipkin's results show that we must distinguish 

 between sex determiners responsible for the F/M balance and modi- 

 fiers affecting special developmental processes (to be discussed in 

 a later chapter). Thus far, no facts are available which would permit 

 localizing the male factors with certainty in intercalary heterochro- 

 matin of the third chromosome. But it is at least significant that the 

 transformer locus (tra, 3.43^5.5), which in homozygous condition 

 transforms genetic females into almost males (extreme female inter- 

 sexes) is located in a region with an accumulation of Minutes, and 

 in or near heterochromatic sections (fig. 9). Lebedeff's (1939) 

 powerful intersexuality factor in D. virilis has a similar localization. 



Moreover, there are a number of indirect signs indicating the 

 heterochromatic nature of the autosomal male determiners. We re- 

 member that there is a strong suspicion that the Minutes are hetero- 

 chromatic mutants (deficiencies). One of the characteristics of these 

 mutants is a tendency to change the male genital armature, which 

 has to be interpreted as beginning intersexuality, that is, weakening 

 of the male determiners (details in Goldschmidt, 1949fl, 1951Zj). We 

 remember further that the mutant Beaded shows heterochromatic 

 features, being able to replace the action of Y heterochromatin in 

 pod K. Bd and the Minutes interact strongly so far as all Minutes 

 enhance the penetrance (and expressivity) of Bd from a small per- 

 centage in Bd/-|- to 100 per cent. The combination of Bd with some 

 Minutes produces a peculiar low-grade and characteristic type of 

 intersexuality in males (Goldschmidt, 1949a). All this taken together 

 suggests strongly the heterochromatic nature of the male determiners. 



In the same experiments was found (Goldschmidt, 1951fo) an- 

 other feature that adds to the indirect evidence. It could be shown 

 that the genetic control of intersexuality by the Bd-M combination, 

 the weakening of the action of the male determiners, takes place 



