If dominant is D and recessive is R there is 3 ways they can divide and come together DD DR RR. Good traits are usually dominant. You cant add by inbreeding you can only take away, so you take away the dross. The recessive. When recessives come together you see the flaw, ie flat feet, cowardice, cow hocks etc. So you cull or remove from programme. The ideal is all traits represented by DD double dominant.