THE STUDY OF IMIKUITANCE 57 



The small fruit fly, Diosophila melanogaster, jifTords excellent 

 material for the study of Mcnddian phenomena. It lays its 

 eggs on fermenting fruit the yeast in which forms the food of 

 both the larva and the adult. The complete reproductive 

 cycle from egg to breeding adult is very short, seldom exceeding 

 two weeks. The Hies cxhil)it a number of different eye colors, 

 body colors, and wing characters the inheritance of which may 

 be studied in the laboratory. They are easily grown in bottles 

 containing fermenting bananas. 



It will be impossible for the student to carry on the actual 

 i)reeding during the time allowed for laboratory work but the 

 steps necessary for the preparation of the material are here given 

 that the process and aims may be better understood. 



Each group of four students should be supplied with a culture 

 of Fi flies produced by crosses involving a single Mendelian fac- 

 tor, such as vestigial wing or sepia or scarlet eye, also samples of 

 the Pi and Fi ancestors as well as larvic and pupaj, the object 

 being that of studying the structural peculiarities of larvae, 

 pupae, and adults and to observe the inheritance of these factors 

 through two generations and compare the actual count of individ- 

 uals in the F2 generation with the expected Mendelian 3:1 

 ratio. These cultures were produced in the manner set forth in 

 the paragraphs which follow. 



Securing the Fi Generation. — Mrgin females for mating were 

 obtained by isolating pupte in individual half-pint milk bottles 

 containing a banana agar-agar preparation for food. Females 

 cannot be taken from the general stock, as they have almost 

 certainly been fertilized by the males in the culture. In order 

 to secure a pair for the first mating (the P, generation) a single 

 pupa was taken from each of the two cultures to be crossed, one 

 from the wild type (red eyed) and one from the sepia-eyed type. 

 Since sex cannot be recognized in the pupal state there are four 

 chances as regards the results, namely, (1) getting a female wild 

 and a male sepia, (2) a male wild and a female sepia, (3) two 

 females, (4) two males. The first two are sati.sfactory for si^cur- 

 ing the Fi generation; if each of the two females resulting from 

 the third possibility is given a male from the original culture 

 these will form two more combinations from which to secure the 

 desired crosses; the two males wliich may result from the fourth 

 chance is the only combination which is not usable for the purpose 

 of this study. After a pair lias been together in the breeding 



