288 



TABLE II. 

 Fj Flies of the Cross, Scarlet Male by Wild Female. 



In the F: generation from the scarlet female (Table I), there was 

 a total of 3,843 wild type flies and 1,132 scarlet, which is approximately 

 a ratio of 3 wild type to 1 scarlet. In the F2 generation from the scarlet 

 male (Table II), there were 8,242 of the wild type and 2,524 of the 

 scarlet, which makes a ratio of 3.22 wild type to 1 scarlet. The extracted 

 scarlets have since bred true. 



Crosses were made to scarlet with the Fi- wild type flies from both 

 the original cross and its reciprocal. To insure virgin flies the sexes 

 were separated every twelve hours. These back-crosses were made in 

 pairs to determine how many of the flies of this generation were homo- 

 zygous and how many were heterozygous. If the scarlet eye-color is a 

 simple recessive unit, all the homozygous blacks mated to scarlet should 

 give only wild type offspring, while the heterozygous blacks mated to 

 scarlet should give equal numbers of blacks and scarlets. The results 

 of these crosses are shown in Tables III to VI. 



Table III gives the results of back-crossing to scarlet the F2 female 

 wild type flies from the original parents, scarlet female by wild male. 

 This table shows that 82 such matings were made. Of these 8? females, 

 27 proved to be homozygous and 55 heterozygous, a ratio of two to one. 

 Table IV, showing the reciprocal cross of Table III, gives 18 homozygous 

 and 59 heterozygous. Table V gives the results obtained by back-cross- 

 ing to scarlet the F^. wild type female from the original parent cross 

 scarlet male by wild female. Of these females, 25 proved to be homo- 



