NON-DISJUNCTION OF SEX CHROMOSOMES 603 



tance between the factors, for example, if A and B give 20 per 

 cent of crossover and A and C give 10 then B and C .will give 

 approximately^ either 20 + 10 or 20 — 10 as the percentage of 

 crossover. Suppose the experiment gives 10 per cent. Then 

 the order becomes A, B, C, and not A C B. This order when 

 once discovered is found to hold when tested out with any other 

 sex-linked factor. If we know how far a new factor D is from 

 A and B we can predict the percentage of crossover of C — D, 

 or if we know its distance from A and C we can predict B — D. 

 At present the series of known sex-linked factors numbers twenty- 

 eight. So far as tested, these factors behave as though they 

 occupied loci in a linear series ivith fixed order and distances, and 

 we believe that this behavior is explicable on the view that the 

 sex chromosome is the material basis of the series. 



The bearing of non-disjunction upon this question is that the 

 series of factors which has been shown to be linear, behaves here as 

 though it were a unit. The whole series that the mother bore 

 descends to her matroclinous daughters, and the whole series of 

 the father to his patroclinous sons. 



It will have been noticed that in all these cases of non-dis- 

 junction, sex behaves in a fashion strictly parallel to that of any 

 sex-linked character. The non-disjunctional eosin or white female 

 transmitted her femaleness to her matroclinous daughters in ex- 

 actly the same manner that she transmitted her eosin or white 

 eyes. This behavior requires' a common vehicle for the trans- 

 mission of sex and a linear series of sex linked characters, and 

 such a vehicle is furnished by the sex chromosome. 



If we accept the conclusion that the matroclinous daughters 

 are the result* of the fertilization of two-X eggs by the no-X 

 spermatozoa, and the patroclinous sons are the result of the fer- 

 tilization of no-X eggs by one-X' spermatozoa, then we must 

 inquire what would result from the fertilization of the two-X 

 eggs by the one-X spermatozoa, and from the fertilization of the 

 no-X eggs by the no-X spermatozoa. In the first case an indi- 

 vidual with three, and in the second case with no sex chromo- 



^ Inaccurate for long distances because of double crossing over. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 15, NO. 4 



