A THIRD SEX-LINKED LETHAL FACTOR IN 

 DROSOPHILA 



T. H. MORGAN 



Department of Zoology, Columbia University 



THREE FIGURES 



In an experiment (reported in the Jour. Exp. ZooL, page 390, 

 November, 1911) in which three sex-Hnked characters were in- 

 volved, namely, white eyes, vermilion eyes and miniature wings, 

 certain results were obtained involving double crossing-over. 

 The more recent results indicate that double crossing-over was 

 excessive in this experiment. ^ A white miniature male had been 

 mated to a vermilion pink ('orange') female. The daughters were 

 wild type (red, long) and the sons vermilion (long) . The two sex- 

 chromosomes of these daughters contain respectively the genes 

 for white (w), red (V), and miniature (m); and for red (W), and 

 vermilion (v), and long (M). All later work has shown the order 

 of the genes here involved is white, vermilion, miniature, as shown 

 in diagram 1. 



On this basis, the results of the previous experiment in terms of 

 cross-overs would be as follows : 



Non-cross-overs (vermilion and ver. pink males) 

 Single cross-overs between white and vermilion 



(min. and min. pink males) 



Single cross-overs between vermilion and min. 



(verm. min. and ver. min. pink males) 



Double cross-overs (wild type and pink males) . . . 



Instead of giving fewer double cross-overs than singles, accord- 

 ing to expectation, the number of doubles was twice that of singles, 

 and for numbers as large as these this difference cannot be due to 



^ In the analysis on page 392 the large C in 'sperm no X' should be small c. This 

 change adds eight classes to the white males and eliminates the same number from 

 the colored classes. The expected numbers in the male classes at the top of page 

 393 should read downwards : 3-3-1-1-8-3-3-1-1-8. 



315 



THE JOURNAL OP EXPERIMENTAL ZOOLOGY, VOL. 17, NO. 3 

 OCTOBER, 1914 



