MENDELISM AND SELECTION 



original stock, and (2) to secure extensive and 

 uniform silvering on a black background. In 

 both these objects good progress has been 

 made. We have animals which are silvered all 

 over the body except on a part of the head, 

 and the percentage of such well-silvered indi- 

 viduals is relatively high. 



But the most extensive selection experiment 

 which I have personally observed is one in 

 which I have been assisted by Dr. John C. 

 Phillips (see Figs. 39 and 41). Selection in 

 this case has been directed toward a modifica- 

 tion of the color pattern of hooded rats, — a 

 pattern which is known to behave as a reces- 

 sive Mendelian character in crosses with either 

 the self (totally pigmented) condition or the 

 so-called Irish (white-bellied) condition found 

 in some other rats. The extreme range of 

 variation among our hooded rats at the outset 

 of this experiment is indicated by the grades 

 — 2 and -f 3 of Fig. 39. Selection was now 

 made of the extreme variates in either direc- 

 tion and these were bred separately. Two 

 series of animals were thus established, — one 

 of narrow striped animals, minus series; the 



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