OF MUTANT CHARACTERS. 



2G1 



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

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

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

 was 766, which is 67.3 per cent of the total nunihor, wlioro 66.7 per 

 cent are expected according to the lethal assumption. 



Table 110. — Fi star 9 + Fj star cf . 



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 iniks.s- 

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

 Likewise none of the star flies selected for out-crossing on ver>' 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 homoz}-gous. 



