The correct answer is Inbreeding. When breeding is between animals of the same breed for 4 - 6 generations, it is called inbreeding. Examples: breeds of cows, buffaloes, poultry etc. Superior cows and superior bulls of the same breed are identified and mated. The progeny obtained from such mating are evaluated and superior males and females are identified for further mating. Thus inbreeding is necessary if we want to develop a pure line in any animal.