ON COUPLING OF CERTAIN SEX-LINKED 

 CHARACTERS IN DROSOPHILA. 



JOHN S. DEXTER. 



In the course of his experiments on the modes of inheritance 

 in Drosophila, Morgan has called attention 1 to the fact that when 

 flies bearing two or more pairs of characters of certain sorts 

 are crossed, these characters appear in the F 2 generation coupled 

 as in the original combination (i. e., in the grandparents). This 

 coupling is not complete, but is much larger than is to be expected 

 if the different pairs of characters were independently mendel- 

 izing. In a letter to me last autumn he suggested that ' in 

 order to find out if there is here some deep-lying principle or 

 only some irregularity, it will be necessary to obtain very large 

 numbers of the Fo's; let us say ten or twenty thousand." 



Morgan has offered an explanation of this coupling 2 on the 

 supposition that the factors concerned in the production of the 

 characters lie near together in the chromosomes, and that the 

 twisting of homologous chromosomes about each other in the 

 strepsinema stage of gametogenesis which causes both maternal 

 and paternal characters to lie on each side of the double chromo- 

 some, does not separate certain factors that lie very close 

 together, so that when the chromosomes split, these factors will 

 both occupy the same gamete. 



It was in order to test these theories that I undertook, at Dr. 

 Morgan's suggestion, to raise " large numbers of the F2*s." 



Dr. Morgan's kindly advice and aid have helped me a great 

 deal in this work. I wish also to record here and express my 

 appreciation of the enthusiastic assistance of Miss Margueritte 

 Harmon and Mr. Felix Gustafson, without whose aid the work 

 could not have been done at this time. 



I began with pure stock of Drosophila of two kinds: Flies with 

 normal body color and red eyes (this is the normal wild fly), 



1 Jour. Exp. Zoo/., Vol. n, No. 4, Nov., 1911, p. 393. 



2 Science, N.S., Vol. 34. No. 873, Sept., 1911, p. 384. 



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