Genie and Non-genic Parts of the Chromosome 93 



in the egg before maturation (so-called maternal effect). Now we 

 know that in Lymantria the Y-chromosomal sex determiners act in 

 the same way; we know further that some of the podoptera factors 

 act in the same way, and that some of the podoptera factors assumed 

 to be heterochromatic (in pod H) also show the maternal effect. In 

 addition, it is known (Sturtevant, 1946) that intersexuality produced 

 in species (geographic "species" or subspecies) crosses of members 

 of the Drosophila repleta group is based upon an autosomal dominant 

 acting upon the egg cytoplasm before fertilization, a maternal effect. 

 Finally, such a maternal effect in sex determination has been found 

 also in plants (Streptocarpus: Oehlkers, 1938, 1940, 1941) in which 

 a close parallel to the analysis of intersexuality in Lymantria was 

 established (further details, and differences, to be discussed in a 

 later chapter). Hence no doubt can exist that we are dealing here 

 with a phenomenon of basic importance. All this adds up to a 

 rather strong argument in favor of our conclusion that sex determina- 

 tion is actually a function of intercalary heterochromatin, a general- 

 ized function, not capable of being dissolved into sets of multiple 

 genes with special actions. 



One more very powerful argument is worth consideration. (See 

 discussion in Goldschmidt, 1950^7.) We remember the mottled po- 

 sition effect which is produced by heterochromatic breaks in the 

 general vicinity of a known locus. Now position effect alone means 

 that a non-mutated locus acts like a mutant when the chromosomal 

 pattern near it is shuffled. The additional mottling in the special 

 cases means that the mutation imitating position effect is not pushed 

 above the threshold of action in a number of cells (which remain 

 wild type). The number of such cells as well as their distribution 

 can be influenced by additional heterochromatin. Altogether, the 

 lesion of a segment of intercalary heterochromatin affects a quantita- 

 tive feature of development so as to reach or not to reach a threshold 

 value. (Similar facts are contained in McClintock's work, as analyzed 

 in my paper, 1950fo. ) The facts known in regard to sex determination 

 may be considered as being of the same general type. Intersexuality 

 in Lymantria and other organisms with a comparable genetic method 

 of sex determination (e.g., Drosophila) means that, as a result of 

 disturbed balance of the female and male sex determiners, develop- 

 ment starts with the chromosomal sex but continues after a definite 

 time, the turning point, with the opposite sex. In many cases this 

 is a simple all-or-none affair, and all development after the turning 

 point is of the opposite sex. But in certain cases, as in Lymantria 



