34 A MANUAL OF MENDELISM 



fawns in the ratio 9:3:3:1, showed that there was 

 really another pair of factors operating. Since it is the 

 largest group in a set of four, black must carry two 

 dominants at least. One may be the factor Y, which it 

 is already known to carry, and the other a new factor, 

 say Z. Nay, both may be new ; and, if they be called 

 Z and A, then the characters carried by the four groups 

 in the set should be : 



Black ZA 



Blue Za 



Chocolate zA 



Silver-fawn za 



Then the total characters carried by black and 

 chocolate, as found by both experiments, should be : 



Black xYZA 



Chocolate xyzA 



But, thus, black and chocolate would differ in two pairs 

 of characters, whereas both experiments show them to 

 differ in one only. Black carries only one new domi- 

 nant therefore ; and, if it be called Z, the characters 

 now known to be carried by black are xYZ. At the 

 same time chocolate must also carry Z, for it already 

 carries xy, and if it carried any other character than Z 

 it would differ from black in more than one pair of 

 characters. 



Since Y and Z and their recessives y and z are the 

 characters combining to form the four colours in the 

 second experiment, and, since blue is shown to be a 

 middle group and silver-fawn the last group, the 

 characters now known to be carried by the four groups 

 in the set are : 



