Page:The Evolution of British Cattle.djvu/108

 The following table shows the average numbers of calves of each of these colours that may be produced by all the possible matings:—

Thus it will be seen that, although by crossing white cattle and red a new colour, roan, is produced, that new colour itself is unstable and throws back constantly to one or other parent race. A similar result follows when white cattle are crossed with black: the intermediate hybrid, as it is called in Mendelian phraseology, being in this case a blue roan.

But, although these intermediate hybrids are unstable, they may be the means of transferring the colour of one kind of cattle from that kind to another kind. The transference of the white colour of the Roman cattle to the black Welsh cattle is a simple case. A white Roman bull breeds with black Welsh cows and produces blue-roan calves. These again breed together, and 25 per cent, of their calves are white. In other respects some of these white calves are Romans, some Welsh, and thus, in two generations only, some black Welsh cattle may be turned white.

Perhaps, for exposition's sake, a more striking