76 



E, CARLETON MACDOWELL 



TABLE 9 



Showing that low and high grades of extra bristles give the same results when crossed 

 with wild normals; also that reciprocal crosses shoiv that no sex linkage is 

 involved 



Low d^c? X Wild 9 9 . 



Low 9 9 X Wild d" cf 



High d^cT X Wild 9 9.. 

 High 9 9 X Wild d'd'.. 



KATIO 



NORM All 



TO 



EXTRA 



3.4:1 

 2.8:1 

 3.3:1 

 3.3:1 



LO\A/Q>^WIL0 oi"__ 



HIGH cAwn.0 Q 



H 1 aH 5 XWILO O* . 



Fig. 4 Extracted exti'a bristles appearing in Fo of reciprocal crosses of high 

 and low grades of extra bristles with normal wild, showing that there is no facto- 

 rial difference between the high and low grade extras crossed. 



2. RESULTS OF SELECTION 



a. Total generations 



On the basis of the conclusions just reached, we should expect 

 to find selection effective in the first few generations and later, 

 ineffective. Data will be presented to show the results of 

 selection in the form of curves for total generations and for single 

 lines. Owing to the difficulty of obtaining high grade females 

 that were unquestionably virgin, the most rigid selection was 

 not always possible, so that even in the later generations some 

 matings were made of low parents. In order to avoid the 

 possibility of hiding a real increase in the offspring from high 

 grade parents by including the offspring from low grade parents, 



