HEREDITY AND VARIATION 



67 



quickly separate the two bottles and stopper the etherizing bottle. 

 When the flies have been quiet about a minute they can be emptied 

 onto a piece of white paper. If the flies begin to move place them in the 

 etherizing bottle again. Classify these flies of the first filial or F^ 

 generation with respect to the character with which you are dealing 

 and as to sex. Make a record of the number in each class. If all 

 the flies are alike with respect to the character being studied their 

 appearance identifies the dominant expression of the character; the 

 alternate state of the character, or the one which does not appear, is 

 recessive. 



(e) The flies that emerge from the isolated pupal cases are to be 

 mated in pairs in culture bottles as before in order to obtain a second 

 filial or Fj generation; make two cultures. Record observations on 

 time of appearance of larvae, pupse, and adults. Again, remove the 

 parent flies after seven or eight days. Eight or nine days after adults 

 of the second generation first emerge, kill, classify for character and 

 sex, and count the progeny as for the first filial generation. 



(f) If time permits make two additional cultures, using for one 

 parent a fly of the first filial generation and for the other a fly of the 

 mutant or recessive stock which was used in the original cross. This 

 is known as a backcross with the recessive type. Make observations 

 and records as specified in (e). 



(g) Tabulate the data gathered in this experiment in the form of 

 a table as shown in Fig. 34. 



(Enter name of recessive 



Fig. 34. — Table for recording data collected in Exercise 2. 



