62 A MANUAL OF MENDELISM 



Similarly, if the hybrids were mated with their white 

 parents, the materials offered should be : 



By the Hybrids By the Whites 

 X X 



.X X. 



.Y Y. 



•y Y. 



and equal numbers of the four following kinds should be 

 produced, three of which should be hybrid in one or both 

 pairs of characters : 



Xx Xx XX XX 



YY Yy YY Yy 



Again, instead of this only two kinds were produced, 

 namely, 34 hybrid blues and 20 true-breeding whites. 



Thus there are not more than one pair of factors in 

 operation. 



With this solution of the Blue Aldalusian problem 

 several questions come to the surface without, as yet, 

 findiag a clear answer, as, for instance : Is blue the result 

 of mating black with white or with grey or A^dth white and 

 grey combined ? If with either white or grey, what becomes 

 of the white or grey splashing which should appear in 

 the hybrids' progeny ? If with white and grey combined, 

 is the same pattern carried by all three colours, but obscured 

 in the white partially and entirely in the black ? 



In addition to white, there are four true-breeding colours 

 among cattle and a still larger number which do not 

 breed true. These true-breeding colours are black, red, 

 light or steel dun, and brown, a colour foimd among 

 Longhoms, Highlanders, and Ayrshires, as well as among 



