550 



MARY B. STARK 



Nine of the daughters were mated individually to white eyed 

 males and gave the results in table 13. 



All nine daughters gave a 2 : 1 ratio which is expected if 

 their mother had two lethals. 



Ten other daughters (from the very high ratio mother) were 

 mated to their red eyed brothers^ and gave the results in table 

 14. 



Six red females of table 13 were tested and gave the following 

 results : 



CROSSING OVER 



BETWEEN WHITE 



AND LETHAL 



7.8 

 12.0 

 15.4 



SEX RATIO 



2.3 :1 

 2.6 :1 

 1.8:1 



Three of the sisters by brother No. 1 failed to produce anj^ 

 progeny when transferred to separate bottles. Each of the other 

 sisters, however, showed the presence of a lethal factor. Thus 

 all 19 daughters of the female gave a 2 : 1 ratio. There can be 

 no question but that the Mgh sex ratio of the mother was due 

 to two lethals. Virgin red eyed daughters of some of these 

 females were then mated to white eyed brothers with results 

 as shown in table 15. 



Since the mothers of the females used in table 15 were all 

 heterozygous for white and for one or the other lethal, they 

 would, when mated to red eyed males, produce two kinds of 

 daughters; one-half heterozygous for a lethal and the other half 



^ If the sons that came through were due to crossing over, then the X chromo- 

 some that went into each is free from lethals and consequently they must be 

 normal males. The normality of these three males was also tested by mating 

 them to wild females. The sex ratio was normal. The daughters of the three 

 males were tested individually and gave normal ratios. 



