OF MUTANT CHARACTERS. 



261 



which ratio was really present. These further cultures left no doubt 

 that the ratio was really the 2 : 1 ratio corresponding to a dominant 

 lethal when homozygous. The total number of stars in such cultures 

 was 766, which is 67.3 per cent o the total number, where 66.7 per 

 cent are expected according to the lethal assumption. 



TABLE 110. FI star 9 + FI star rf 1 . 



TABLE 111. PI, star cf X peach sooty 9 . 



The history of the stock likewise proved the lethal nature of the 

 homozygote; for star flies were inbred for many generations in mass- 

 culture without giving any closer an approach to a pure-breeding stock. 

 Likewise none of the star flies selected for out-crossing on very numer- 

 ous occasions ever proved to be homozygous; all gave the 1 : 1 ratio 

 typical of a heterozygous dominant. Lately, much more vigorous 

 tests have conclusively proved that star is lethal when homozygous. 



