38 A MANUAL OF MENDELISM 



sides. Thus, since grey parents have black progeny, 

 grey is apparently dominant to black. 



In the course of his experiments, which are reported 

 in vol. xxix of the Journal of the Linnean Society, 1904, 

 Mr. Hurst bred both grey and black rabbits which bred 

 true ; and, when they were mated, their hybrids were 

 all grey, while the hybrids' progeny were greys and 

 blacks in the ratio 3 : 1 (actually 38 : 10). Thus the 

 inference that grey is dominant to black is confirmed ; 

 and, symbolizing the two colours by their initial letters, 

 we may write down the one-pair set of two groups in 

 the usual way, as follows : 



G b j 



3:1 j 



But Professor Castle's experiments, which are sum- 

 marized in Science, vol. 26, 1907, show this solution 

 to be far too simple, for he found six colours intermate- 

 able, grey and black both included : a result indicating 

 three pairs of factors in operation and two more colours 

 remaining to be found. Among the six colours, the 

 following relationships are recorded : 



(1) Grey is dominant to blue-grey, black, and yellow. 



(2) Blue-grey is dominant to blue. 



(3) Black is dominant to blue and tortoise-shell. 



(4) Yellow is dominant to tortoise-shell. 



(5) Grey is got by crossing black with either blue-grey 

 or yellow. 



By being dominant to three other colours, grey must 

 carry three dominant characters, and, by being recessive 

 to it and differing from it therefore in one pair of 

 characters, each of these three colours must carry two 

 of the dominants carried by grey, together with the 



