368 



GENES MODIFYING NOTCH. 



THIRD TEST. 



In the second generation of the first test there were some eosin 

 Star Dichsete males whose X chromosome should be the same as that 

 of the Fi males. Since the second and third chromosomes appeared 

 not to affect the result in the first test it should not be expected to 

 affect the result here, whichever ones are present. Half of the sperm of 

 the males, however, should carry one of the fourth chromosomes of the 

 short-Notch mother; the other fourth chromosome would be in half 

 of the flies derived from the same source and in half from the Star- 



Dichsete grandparent. If the fourth chromosome causes the differ- 

 ence between the short-Notch and the atavistic type it would be 

 expected that some of the males crossed to short-Notch females would 

 give one result and some another (3:1). There were five cultures with 

 both atavistic and short and one with short Notch only. It is doubtful 

 if this should have any significance (although it tallies wdth the expec- 

 tation) because it is not absolutely certain that in all of them only 

 one male fertilized the female. The next test was decisive, so that it 

 was not necessary to repeat the experiment. 



