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 pan* of factors in 

 operation. 



With this solution of the Blue Aldalusian problem 

 several questions come to the surface without, as yet, 

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

 of mating black with white or with grey or with 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 found among 

 Longhoms, Highlanders, and Ayrshires, as well as among 



