I'll try and have a go at it, Take a 3/8 - 5/8 bull/grey dog over a 3/8 - 5/8 leghorn/grey bitch. Now for the puppies there 3/8 bull blood total, So devide that in half = 3/16. There 5/8 grey in the cross twice, once from the dog, once from the bitch, take half on that which is 5/8. That leaves 3/8 leghorn devided in half = 3/16. This leaves you with a pup that is 3/16 bull, 5/8 greyhound, 3/16 leghorn. Not enough leghorn to lay eggs, but enough that they can really fly.