JOHN W. GOWEN 



Iowa Stafe College 



Chapter 29 



Hybrid Vigor in 

 Drosophila 



Experience has defined hybrid vigor as the evident superiority of the hybrid 

 over the better parent in any measurable character as size, general vegetative 

 vigor, or yield. For any one species it is left for us to show that, within the 

 possible crosses of pure lines, hybrid vigor actually exists and what particular 

 morphological and physiological characters express it best. 



With this in mind, investigations with wild-type Drosophila of diverse 

 geographical origin were begun in 1934 and continued to date. The group 

 working on this problem has included Dr. Leslie E. Johnson, Dr. F. S. Straus, 

 Miss Janice Stadler, Dr. S. Y. Loh, and myself. The material reported here 

 is the result of our joint efforts. To specify the problem of hybrid vigor, five 

 characteristics were chosen for investigation in eight inbred lines of Drosoph- 

 ila and a hybrid between two of the lines. The characteristics chosen were 

 egg production throughout the full life of the fly, the days the females laid the 

 eggs, the hatchability of the eggs, and the duration of life of the males and 

 females in each line. 



To determine egg production, a pair of flies of a particular line was placed 

 in a quarter-pint milk bottle sealed with a paraffin paper cap on which was 

 placed a disk of nutrient banana agar colored with charcoal. The female laid 

 her whole day's egg output on this disk when it was properly seeded with 

 yeast and a little acetic acid. The caps, a sample shown in Figure 29.1, were 

 changed daily and the eggs were counted for each day. 



The characteristic performances of the different pure lines and the hybrid 

 are shown in Table 29.1. 



The average egg production for the different inbred races varied from 263 

 to 1701 eggs. There is some correlation between the intensity of the inbreed- 

 ing and the production of the particular race. Ames I and II are less inbred 



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