1917 



EXTOMOLOGIOAL SOCIETY 



71 



EXPEUIMKXTS WITH TlIK PoMACE FlY, 



Morgan's recent investigations Avith hybrids of Drosophila ampelophila, the 

 common pomace fly, have added much to our knowledge of factors in heredity. 

 He found that each visible character is. due to the action of a number of factors 

 in the germ plasm, each factor in turn influencing a large number of other traits. 

 Moreover, these factors are linked together in grof.ps, in chromosomes, where they 

 are arranged in a linear series, sometimes changing places by crossing over. With 

 Drosophila, which was normally red-eyed, there appeared in the course of breed- 

 ing experiments as mnny as 25 distinct mutations in this eye-color. Morgan 

 supposes, therefore, that at least 25 factors are concerned in the production of this 

 red eye, and that when a single one changes a different color is obtained. This 

 one factor, however, may be called the unit factor for this particular color, so it 

 may be treated in a simple Mendelian factor in segregation. The following 

 examples illustrate one of the simpler cases of inheritance : 



Case I. Red-eyed (female) with white-eyed (male). 



rF rf = male gametes. 



Female 

 gametes 



RF 

 RF 



Progeny all red-eyed. 



The diagram of the Fj generation is : 



RF rf 



RF 



Female 

 gametes 



rF 



= male gametes. 



= 50% red-eyed females. 

 25% red-eyed males. 

 25% white-eyed males. 



Ca.se //. White-eyed (male) x Fi red-eyed female (heterozygous), 

 rF rf = male gametes. 



Female 

 gametes 



Red-eyed 

 RF female 



Red-eyed 

 male 



rF 



White-eyed White-eyed 

 female male 



= 25% red-eyed females. 



25% red-eyed males. 



25% white-eyed females. 



25% white-eyed males. 



Case III. Eed-eycd (male) x wliite-cyed (female). 



RF rf := male gametes. 



Female 

 gametes 



= 50% red-eyed females. 

 50% white-eyed males. 



showing that the red-eyed male parent is heterozygous for color. 



